investigation of microstructure and mechanical properties
TRANSCRIPT
Investigation of microstructure and mechanical properties of thermally aged Alloy 600
Seung Chang Yoo
with significant contributions from
KJ Choi T Kim S Kim and JHKim Corresponding author Ji Hyun Kim (kimjhunistackr)
School of Mechanical and Nuclear Engineering Ulsan National Institute of Science and Technology (UNIST) Ulsan Republic of Korea
Presented at 17th International Conference on Environmental Degradation of Materials in Nuclear Power Systems ndash Water Reactors
Fairmont Chateau Laurier Ottawa Ontario Canada August 10 2015
Outlook
1
2
3
4
Background
Objective and Approach
Experiment
Results and discussions
5 Summary
Materials used in the primary circuit of nuclear power plants (NPPs) are exposed to a very challenging environment of high temperature stress vibration radiation and corrosive water
Head penetration nozzles for the control rod drive mechanism (CRDM) of the reactor pressure vessel suffers from a number of cracking and coolant leak incidents in recent years mainly due to primary water stress corrosion cracking (PWSCC)
Addition to this the issue of material degradation by long-term thermal aging by increased operational life of NPPs make it issued as an important factor in evaluating the safety and reliability of NPP in long-term operation
However the effect of long-term exposure to relatively low temperature (300~400) to material degradation which is similar to real situation in NPPs have not been investigated fully
The potential for material degradation of head penetration nozzles have been emphasized and the influence of long-term thermal aging to the susceptibility of material degradation for this part have not been clarified Therefore to understand the change of material properties and PWSCC resistance by long-term thermal aging basic microstructures and mechanical properties are investigated in this research
3
Background (11)
Introduction
Objective Investigate the effect of long-term thermal aging to PWSCC initiation resistance of material (preliminary study) Investigate the variation of detailed microstructural and mechanical
properties of the Alloy 600 subjected to long-term thermal aging in an operating NPP to evaluate the influence of long-term thermal aging to material property
Approach Thermal aging simulation of light water reactor environment at accelerated temperature
Microstructural analysis with Electron Microscopy Electron Backscattered Diffraction (EBSD)
Mechanical property analysis with Tensile test Nanoindentation
IGSCC resistance analysis with huey test
4
Objective and Approach
Objective and Approach
Alloy 600 thick rod specified by ASTM B166 was provided by Doosan Heavy Industries amp Construction Annealed at 1060 for 35 h and water quenched
Accelerated temperature was determined as 400oC and for activation energy of Cr diffusion at grain boundary 180 kJmol was used for Ni base alloy which containing 15 to 30 wt chromium [1]
5
Experiment (12)
Material amp Thermal aging
Chemical compositions (wt)
Element C Si Mn Cr Cu Ni S Fe
wt 007 033 056 1583 002 7479 lt0001 840
Heat treatment and aging conditions of each specimen Specimen name Simulated aging time and temperature Heat treatment time and temperature
As-received - - HT400_Y10 10 years at 320 1142 hours at 400 HT400_Y20 20 years at 320 2284 hours at 400
119905119886119886119886119886119886119905119903119903119903
= 119890119890119890 minus119876 1
119879119903119903119903minus 1119879119886119886119886119886119886
119877
119905119886119886119886119886119886 119905119903119903119903 119879119886119886119886119886119886 119879119903119903119903
R 119876
= Heat treatment time [h] = Simulated aging time [h] = Heat treatment temperature [K] = Simulated aging temperature [K] = Gas Constance [=8314 JmolK] = Activation Energy for Cr diffusion [kJmol]
Diffusion equation for thermal aging
[1] JM Boursier et al ASME PVP (2004)
6
Experiment (22)
Conditions Experiment conditions
EBSD Acceleration voltage 10 kV Current 064 nA Tilt angle 70deg Step size 2 μm Scanned area 298 μm x 881 μm to cover several number of grains
Nanoindentation Poisson`s ratio 03 Strain rate 005 sec-1
Displacement into surface 2000 nm using berkovich tip To improve the reliability of the results an average was taken from multiple indentations
at random position of matrix Tensile test
Multiple tests were performed at strain rate of 04 sec-1 at room temperature Test were prepared and performed based on ASTM E8-E8m
Huey test 20 cm3 was exposed to 80oC 65 HNO3 solution for 96 hours and weight loss of each
specimens were measured Test were prepared and performed based on ASTM A262
Proportionally reduced specimen from ASTM standard used in tensile test
Specimen As-received HT400_Y10 HT400_Y20
Young`s modulus [GPa] 2113 plusmn 120 2907 plusmn 119 2567 plusmn 464
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
7
Results and discussions (18)
Tensile test
bull At the engineering stress-strain curve hardening occurred by 10 years thermal aging while softening occurred by 20 years thermal aging
Representative stress-strain curves of each specimen
8
Results and discussions (28)
Tensile test
bull At fracture surface of each specimen typical ductile failure mode with many dimple were observed It is hard to quantify the size of dimple since there size is not unique as small dimples observed in large dimples
bull There exist grain boundary fracture in thermally aged specimens
50μm 50μm 50μm
Fracture surface of As-received Fracture surface of HT400_Y10 Fracture surface of HT400_Y20
30μm 30μm 30μm
9
Results and discussions (38)
Hardness
bull In nanoindentation test same trend with tensile test were observed The hardness was increased by 10 years thermal aging and decreased by 20 years thermal aging
bull Hardness at grain boundary have slightly higher value for all specimens however the difference was not significant in order of 005 GPa It is because the plastic deformation zone of indentation is large (~25um) enough to cover several grain boundaries so influence of precipitates to hardness is almost constant
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 247 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 259 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)Indentation depth (nm)
Mean 281 GPa
Nanoindentation result of As-received Nanoindentation result of HT400_Y10 Nanoindentation result of HT400_Y20
Investigated location As-received HT400_Y10 HT400_Y20
Inside grain [GPa] 244 plusmn 003 275 plusmn 008 255 plusmn 009
Cover grain boundary [GPa] 25 plusmn 002 276 plusmn 005 26 plusmn 01
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
30μm 30μm 30μm
10
Results and discussions (48)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
OM image of As-received OM image of HT400_Y10 OM image of HT400_Y20
200μm 200μm 200μm
11
Results and discussions (58)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
30μm 30μm 30μm
10μm 10μm 10μm
bull The morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
12
Results and discussions (68)
Microstructure
bull The morphology of precipitates were known to have significant influence to material`s mechanical properties And this feature is the main reason for mechanical property changes due to thermal aging
bull The feature of calculated material strength according to Orowan mechanism which explain the amount of hardening due to precipiates shows same trend with that of mechanical test which was conducted in this study hardening by 10 years thermal aging and softening by 20 years thermal aging Therefore it could be thought that the aspect of mechanical properties due to thermal aging is closely related to the morphology of precipitates
Material hardening and softening behavior depending on the number fraction and length of precipitates
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates [] 036 plusmn 004 12 plusmn 01 143 plusmn 014
Precipitate length [μm] 080 plusmn 030 092 plusmn 031 186 plusmn 119
Spacing between precipitates [μm] 278 plusmn 022 192 plusmn 014 328 plusmn 031
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
Morphology of precipitates Discrete Semi-continuous Continuous
Summary of mechanical and microstructural characteristics of each specimen
120533 =119918119918
119923 minus 2119955
[1] Z Guo et al Mater Trans (2002) [2] R Hayes et al Acta Metal (1982)
13
Results and discussions (78)
Microstructure Kernel Average Misorientation
Grain boundary misorientation
Grain boundary misorientation
Grain boundary misorientation
Kernel Average Misorientation
Kernel Average Misorientation
EBSD analysis results of HT400_Y20 EBSD analysis results of HT400_Y10 EBSD analysis results of As-received
200μm 200μm 200μm 200μm 200μm 200μm
bull Kernel average misorientation (KAM) which is proportional to residual strain induced by dislocation density was not much changed by thermal aging
bull Grain boundary misorientation however significantly changed Coincidence site lattice boundary which is more resistant to material degradation was decreased by thermal aging The formation of precipitates could be a reason for this however it could be verified with other tools like TEM
14
Results and discussions (88)
Microstructure
bull Major changes induced by thermal aging were length and morphology of precipitates bull HT400_Y10 have semi-continuous precipitates HT400_Y20 have continuous precipitates and As-received
specimen have discontinuous precipitates bull Several previous studies suggest that material with continuous feature of precipitates have lower
susceptibility to SCC than materials with both semi-continuous and discontinuous precipitates bull With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to
formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates []
036 plusmn 004
12 plusmn 01
143 plusmn 014
Precipitate length [μm] 0801 plusmn 0297
0923 plusmn 0312
1864 plusmn 119
Grain size [μm] 2667 2461 2539
Fraction of CSL boundary []
255 plusmn 38
153 plusmn 488
68 plusmn 441
Morphology of precipitates Discrete Semi-
continuous Continuous
Corrosion resistance by huey test [mmyr] 504 697 523
Average properties in electron microscopy
[1] G S Was Corrosion (1990) [2] J R Crum et al 4th EDM-NPS (1990)
SEM images of each specimen (a) as-received (b) HT400_Y10 and (c) HT400_Y20
(a)
(b) (c)
Thermally aged Alloy 600 was investigated to understand the change of microstructural and mechanical features by long-term thermal aging
In tensile and indentation test material shows hardening at 10 years thermal aging while softening happens in 20 years thermal aging This could be explained by Orowan mechanism that there exist peak strength during precipitate strengthening and softening will occur after that point
bull The morphology of precipitates were mainly changed by thermal aging By 10 years thermal aging length was almost same with as-received but area fraction was significantly increased By 20 years thermal aging length was severally increased and area fraction was not much changed And the morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation This will be verified with PWSCC initiation test which will be conducted in PWR environment
15
Summary
Summary
- Slide Number 1
- Slide Number 2
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 10
- Slide Number 11
- Slide Number 12
- Slide Number 13
- Slide Number 14
- Slide Number 15
- Slide Number 16
-
Outlook
1
2
3
4
Background
Objective and Approach
Experiment
Results and discussions
5 Summary
Materials used in the primary circuit of nuclear power plants (NPPs) are exposed to a very challenging environment of high temperature stress vibration radiation and corrosive water
Head penetration nozzles for the control rod drive mechanism (CRDM) of the reactor pressure vessel suffers from a number of cracking and coolant leak incidents in recent years mainly due to primary water stress corrosion cracking (PWSCC)
Addition to this the issue of material degradation by long-term thermal aging by increased operational life of NPPs make it issued as an important factor in evaluating the safety and reliability of NPP in long-term operation
However the effect of long-term exposure to relatively low temperature (300~400) to material degradation which is similar to real situation in NPPs have not been investigated fully
The potential for material degradation of head penetration nozzles have been emphasized and the influence of long-term thermal aging to the susceptibility of material degradation for this part have not been clarified Therefore to understand the change of material properties and PWSCC resistance by long-term thermal aging basic microstructures and mechanical properties are investigated in this research
3
Background (11)
Introduction
Objective Investigate the effect of long-term thermal aging to PWSCC initiation resistance of material (preliminary study) Investigate the variation of detailed microstructural and mechanical
properties of the Alloy 600 subjected to long-term thermal aging in an operating NPP to evaluate the influence of long-term thermal aging to material property
Approach Thermal aging simulation of light water reactor environment at accelerated temperature
Microstructural analysis with Electron Microscopy Electron Backscattered Diffraction (EBSD)
Mechanical property analysis with Tensile test Nanoindentation
IGSCC resistance analysis with huey test
4
Objective and Approach
Objective and Approach
Alloy 600 thick rod specified by ASTM B166 was provided by Doosan Heavy Industries amp Construction Annealed at 1060 for 35 h and water quenched
Accelerated temperature was determined as 400oC and for activation energy of Cr diffusion at grain boundary 180 kJmol was used for Ni base alloy which containing 15 to 30 wt chromium [1]
5
Experiment (12)
Material amp Thermal aging
Chemical compositions (wt)
Element C Si Mn Cr Cu Ni S Fe
wt 007 033 056 1583 002 7479 lt0001 840
Heat treatment and aging conditions of each specimen Specimen name Simulated aging time and temperature Heat treatment time and temperature
As-received - - HT400_Y10 10 years at 320 1142 hours at 400 HT400_Y20 20 years at 320 2284 hours at 400
119905119886119886119886119886119886119905119903119903119903
= 119890119890119890 minus119876 1
119879119903119903119903minus 1119879119886119886119886119886119886
119877
119905119886119886119886119886119886 119905119903119903119903 119879119886119886119886119886119886 119879119903119903119903
R 119876
= Heat treatment time [h] = Simulated aging time [h] = Heat treatment temperature [K] = Simulated aging temperature [K] = Gas Constance [=8314 JmolK] = Activation Energy for Cr diffusion [kJmol]
Diffusion equation for thermal aging
[1] JM Boursier et al ASME PVP (2004)
6
Experiment (22)
Conditions Experiment conditions
EBSD Acceleration voltage 10 kV Current 064 nA Tilt angle 70deg Step size 2 μm Scanned area 298 μm x 881 μm to cover several number of grains
Nanoindentation Poisson`s ratio 03 Strain rate 005 sec-1
Displacement into surface 2000 nm using berkovich tip To improve the reliability of the results an average was taken from multiple indentations
at random position of matrix Tensile test
Multiple tests were performed at strain rate of 04 sec-1 at room temperature Test were prepared and performed based on ASTM E8-E8m
Huey test 20 cm3 was exposed to 80oC 65 HNO3 solution for 96 hours and weight loss of each
specimens were measured Test were prepared and performed based on ASTM A262
Proportionally reduced specimen from ASTM standard used in tensile test
Specimen As-received HT400_Y10 HT400_Y20
Young`s modulus [GPa] 2113 plusmn 120 2907 plusmn 119 2567 plusmn 464
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
7
Results and discussions (18)
Tensile test
bull At the engineering stress-strain curve hardening occurred by 10 years thermal aging while softening occurred by 20 years thermal aging
Representative stress-strain curves of each specimen
8
Results and discussions (28)
Tensile test
bull At fracture surface of each specimen typical ductile failure mode with many dimple were observed It is hard to quantify the size of dimple since there size is not unique as small dimples observed in large dimples
bull There exist grain boundary fracture in thermally aged specimens
50μm 50μm 50μm
Fracture surface of As-received Fracture surface of HT400_Y10 Fracture surface of HT400_Y20
30μm 30μm 30μm
9
Results and discussions (38)
Hardness
bull In nanoindentation test same trend with tensile test were observed The hardness was increased by 10 years thermal aging and decreased by 20 years thermal aging
bull Hardness at grain boundary have slightly higher value for all specimens however the difference was not significant in order of 005 GPa It is because the plastic deformation zone of indentation is large (~25um) enough to cover several grain boundaries so influence of precipitates to hardness is almost constant
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 247 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 259 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)Indentation depth (nm)
Mean 281 GPa
Nanoindentation result of As-received Nanoindentation result of HT400_Y10 Nanoindentation result of HT400_Y20
Investigated location As-received HT400_Y10 HT400_Y20
Inside grain [GPa] 244 plusmn 003 275 plusmn 008 255 plusmn 009
Cover grain boundary [GPa] 25 plusmn 002 276 plusmn 005 26 plusmn 01
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
30μm 30μm 30μm
10
Results and discussions (48)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
OM image of As-received OM image of HT400_Y10 OM image of HT400_Y20
200μm 200μm 200μm
11
Results and discussions (58)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
30μm 30μm 30μm
10μm 10μm 10μm
bull The morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
12
Results and discussions (68)
Microstructure
bull The morphology of precipitates were known to have significant influence to material`s mechanical properties And this feature is the main reason for mechanical property changes due to thermal aging
bull The feature of calculated material strength according to Orowan mechanism which explain the amount of hardening due to precipiates shows same trend with that of mechanical test which was conducted in this study hardening by 10 years thermal aging and softening by 20 years thermal aging Therefore it could be thought that the aspect of mechanical properties due to thermal aging is closely related to the morphology of precipitates
Material hardening and softening behavior depending on the number fraction and length of precipitates
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates [] 036 plusmn 004 12 plusmn 01 143 plusmn 014
Precipitate length [μm] 080 plusmn 030 092 plusmn 031 186 plusmn 119
Spacing between precipitates [μm] 278 plusmn 022 192 plusmn 014 328 plusmn 031
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
Morphology of precipitates Discrete Semi-continuous Continuous
Summary of mechanical and microstructural characteristics of each specimen
120533 =119918119918
119923 minus 2119955
[1] Z Guo et al Mater Trans (2002) [2] R Hayes et al Acta Metal (1982)
13
Results and discussions (78)
Microstructure Kernel Average Misorientation
Grain boundary misorientation
Grain boundary misorientation
Grain boundary misorientation
Kernel Average Misorientation
Kernel Average Misorientation
EBSD analysis results of HT400_Y20 EBSD analysis results of HT400_Y10 EBSD analysis results of As-received
200μm 200μm 200μm 200μm 200μm 200μm
bull Kernel average misorientation (KAM) which is proportional to residual strain induced by dislocation density was not much changed by thermal aging
bull Grain boundary misorientation however significantly changed Coincidence site lattice boundary which is more resistant to material degradation was decreased by thermal aging The formation of precipitates could be a reason for this however it could be verified with other tools like TEM
14
Results and discussions (88)
Microstructure
bull Major changes induced by thermal aging were length and morphology of precipitates bull HT400_Y10 have semi-continuous precipitates HT400_Y20 have continuous precipitates and As-received
specimen have discontinuous precipitates bull Several previous studies suggest that material with continuous feature of precipitates have lower
susceptibility to SCC than materials with both semi-continuous and discontinuous precipitates bull With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to
formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates []
036 plusmn 004
12 plusmn 01
143 plusmn 014
Precipitate length [μm] 0801 plusmn 0297
0923 plusmn 0312
1864 plusmn 119
Grain size [μm] 2667 2461 2539
Fraction of CSL boundary []
255 plusmn 38
153 plusmn 488
68 plusmn 441
Morphology of precipitates Discrete Semi-
continuous Continuous
Corrosion resistance by huey test [mmyr] 504 697 523
Average properties in electron microscopy
[1] G S Was Corrosion (1990) [2] J R Crum et al 4th EDM-NPS (1990)
SEM images of each specimen (a) as-received (b) HT400_Y10 and (c) HT400_Y20
(a)
(b) (c)
Thermally aged Alloy 600 was investigated to understand the change of microstructural and mechanical features by long-term thermal aging
In tensile and indentation test material shows hardening at 10 years thermal aging while softening happens in 20 years thermal aging This could be explained by Orowan mechanism that there exist peak strength during precipitate strengthening and softening will occur after that point
bull The morphology of precipitates were mainly changed by thermal aging By 10 years thermal aging length was almost same with as-received but area fraction was significantly increased By 20 years thermal aging length was severally increased and area fraction was not much changed And the morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation This will be verified with PWSCC initiation test which will be conducted in PWR environment
15
Summary
Summary
- Slide Number 1
- Slide Number 2
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 10
- Slide Number 11
- Slide Number 12
- Slide Number 13
- Slide Number 14
- Slide Number 15
- Slide Number 16
-
Materials used in the primary circuit of nuclear power plants (NPPs) are exposed to a very challenging environment of high temperature stress vibration radiation and corrosive water
Head penetration nozzles for the control rod drive mechanism (CRDM) of the reactor pressure vessel suffers from a number of cracking and coolant leak incidents in recent years mainly due to primary water stress corrosion cracking (PWSCC)
Addition to this the issue of material degradation by long-term thermal aging by increased operational life of NPPs make it issued as an important factor in evaluating the safety and reliability of NPP in long-term operation
However the effect of long-term exposure to relatively low temperature (300~400) to material degradation which is similar to real situation in NPPs have not been investigated fully
The potential for material degradation of head penetration nozzles have been emphasized and the influence of long-term thermal aging to the susceptibility of material degradation for this part have not been clarified Therefore to understand the change of material properties and PWSCC resistance by long-term thermal aging basic microstructures and mechanical properties are investigated in this research
3
Background (11)
Introduction
Objective Investigate the effect of long-term thermal aging to PWSCC initiation resistance of material (preliminary study) Investigate the variation of detailed microstructural and mechanical
properties of the Alloy 600 subjected to long-term thermal aging in an operating NPP to evaluate the influence of long-term thermal aging to material property
Approach Thermal aging simulation of light water reactor environment at accelerated temperature
Microstructural analysis with Electron Microscopy Electron Backscattered Diffraction (EBSD)
Mechanical property analysis with Tensile test Nanoindentation
IGSCC resistance analysis with huey test
4
Objective and Approach
Objective and Approach
Alloy 600 thick rod specified by ASTM B166 was provided by Doosan Heavy Industries amp Construction Annealed at 1060 for 35 h and water quenched
Accelerated temperature was determined as 400oC and for activation energy of Cr diffusion at grain boundary 180 kJmol was used for Ni base alloy which containing 15 to 30 wt chromium [1]
5
Experiment (12)
Material amp Thermal aging
Chemical compositions (wt)
Element C Si Mn Cr Cu Ni S Fe
wt 007 033 056 1583 002 7479 lt0001 840
Heat treatment and aging conditions of each specimen Specimen name Simulated aging time and temperature Heat treatment time and temperature
As-received - - HT400_Y10 10 years at 320 1142 hours at 400 HT400_Y20 20 years at 320 2284 hours at 400
119905119886119886119886119886119886119905119903119903119903
= 119890119890119890 minus119876 1
119879119903119903119903minus 1119879119886119886119886119886119886
119877
119905119886119886119886119886119886 119905119903119903119903 119879119886119886119886119886119886 119879119903119903119903
R 119876
= Heat treatment time [h] = Simulated aging time [h] = Heat treatment temperature [K] = Simulated aging temperature [K] = Gas Constance [=8314 JmolK] = Activation Energy for Cr diffusion [kJmol]
Diffusion equation for thermal aging
[1] JM Boursier et al ASME PVP (2004)
6
Experiment (22)
Conditions Experiment conditions
EBSD Acceleration voltage 10 kV Current 064 nA Tilt angle 70deg Step size 2 μm Scanned area 298 μm x 881 μm to cover several number of grains
Nanoindentation Poisson`s ratio 03 Strain rate 005 sec-1
Displacement into surface 2000 nm using berkovich tip To improve the reliability of the results an average was taken from multiple indentations
at random position of matrix Tensile test
Multiple tests were performed at strain rate of 04 sec-1 at room temperature Test were prepared and performed based on ASTM E8-E8m
Huey test 20 cm3 was exposed to 80oC 65 HNO3 solution for 96 hours and weight loss of each
specimens were measured Test were prepared and performed based on ASTM A262
Proportionally reduced specimen from ASTM standard used in tensile test
Specimen As-received HT400_Y10 HT400_Y20
Young`s modulus [GPa] 2113 plusmn 120 2907 plusmn 119 2567 plusmn 464
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
7
Results and discussions (18)
Tensile test
bull At the engineering stress-strain curve hardening occurred by 10 years thermal aging while softening occurred by 20 years thermal aging
Representative stress-strain curves of each specimen
8
Results and discussions (28)
Tensile test
bull At fracture surface of each specimen typical ductile failure mode with many dimple were observed It is hard to quantify the size of dimple since there size is not unique as small dimples observed in large dimples
bull There exist grain boundary fracture in thermally aged specimens
50μm 50μm 50μm
Fracture surface of As-received Fracture surface of HT400_Y10 Fracture surface of HT400_Y20
30μm 30μm 30μm
9
Results and discussions (38)
Hardness
bull In nanoindentation test same trend with tensile test were observed The hardness was increased by 10 years thermal aging and decreased by 20 years thermal aging
bull Hardness at grain boundary have slightly higher value for all specimens however the difference was not significant in order of 005 GPa It is because the plastic deformation zone of indentation is large (~25um) enough to cover several grain boundaries so influence of precipitates to hardness is almost constant
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 247 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 259 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)Indentation depth (nm)
Mean 281 GPa
Nanoindentation result of As-received Nanoindentation result of HT400_Y10 Nanoindentation result of HT400_Y20
Investigated location As-received HT400_Y10 HT400_Y20
Inside grain [GPa] 244 plusmn 003 275 plusmn 008 255 plusmn 009
Cover grain boundary [GPa] 25 plusmn 002 276 plusmn 005 26 plusmn 01
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
30μm 30μm 30μm
10
Results and discussions (48)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
OM image of As-received OM image of HT400_Y10 OM image of HT400_Y20
200μm 200μm 200μm
11
Results and discussions (58)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
30μm 30μm 30μm
10μm 10μm 10μm
bull The morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
12
Results and discussions (68)
Microstructure
bull The morphology of precipitates were known to have significant influence to material`s mechanical properties And this feature is the main reason for mechanical property changes due to thermal aging
bull The feature of calculated material strength according to Orowan mechanism which explain the amount of hardening due to precipiates shows same trend with that of mechanical test which was conducted in this study hardening by 10 years thermal aging and softening by 20 years thermal aging Therefore it could be thought that the aspect of mechanical properties due to thermal aging is closely related to the morphology of precipitates
Material hardening and softening behavior depending on the number fraction and length of precipitates
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates [] 036 plusmn 004 12 plusmn 01 143 plusmn 014
Precipitate length [μm] 080 plusmn 030 092 plusmn 031 186 plusmn 119
Spacing between precipitates [μm] 278 plusmn 022 192 plusmn 014 328 plusmn 031
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
Morphology of precipitates Discrete Semi-continuous Continuous
Summary of mechanical and microstructural characteristics of each specimen
120533 =119918119918
119923 minus 2119955
[1] Z Guo et al Mater Trans (2002) [2] R Hayes et al Acta Metal (1982)
13
Results and discussions (78)
Microstructure Kernel Average Misorientation
Grain boundary misorientation
Grain boundary misorientation
Grain boundary misorientation
Kernel Average Misorientation
Kernel Average Misorientation
EBSD analysis results of HT400_Y20 EBSD analysis results of HT400_Y10 EBSD analysis results of As-received
200μm 200μm 200μm 200μm 200μm 200μm
bull Kernel average misorientation (KAM) which is proportional to residual strain induced by dislocation density was not much changed by thermal aging
bull Grain boundary misorientation however significantly changed Coincidence site lattice boundary which is more resistant to material degradation was decreased by thermal aging The formation of precipitates could be a reason for this however it could be verified with other tools like TEM
14
Results and discussions (88)
Microstructure
bull Major changes induced by thermal aging were length and morphology of precipitates bull HT400_Y10 have semi-continuous precipitates HT400_Y20 have continuous precipitates and As-received
specimen have discontinuous precipitates bull Several previous studies suggest that material with continuous feature of precipitates have lower
susceptibility to SCC than materials with both semi-continuous and discontinuous precipitates bull With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to
formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates []
036 plusmn 004
12 plusmn 01
143 plusmn 014
Precipitate length [μm] 0801 plusmn 0297
0923 plusmn 0312
1864 plusmn 119
Grain size [μm] 2667 2461 2539
Fraction of CSL boundary []
255 plusmn 38
153 plusmn 488
68 plusmn 441
Morphology of precipitates Discrete Semi-
continuous Continuous
Corrosion resistance by huey test [mmyr] 504 697 523
Average properties in electron microscopy
[1] G S Was Corrosion (1990) [2] J R Crum et al 4th EDM-NPS (1990)
SEM images of each specimen (a) as-received (b) HT400_Y10 and (c) HT400_Y20
(a)
(b) (c)
Thermally aged Alloy 600 was investigated to understand the change of microstructural and mechanical features by long-term thermal aging
In tensile and indentation test material shows hardening at 10 years thermal aging while softening happens in 20 years thermal aging This could be explained by Orowan mechanism that there exist peak strength during precipitate strengthening and softening will occur after that point
bull The morphology of precipitates were mainly changed by thermal aging By 10 years thermal aging length was almost same with as-received but area fraction was significantly increased By 20 years thermal aging length was severally increased and area fraction was not much changed And the morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation This will be verified with PWSCC initiation test which will be conducted in PWR environment
15
Summary
Summary
- Slide Number 1
- Slide Number 2
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 10
- Slide Number 11
- Slide Number 12
- Slide Number 13
- Slide Number 14
- Slide Number 15
- Slide Number 16
-
Objective Investigate the effect of long-term thermal aging to PWSCC initiation resistance of material (preliminary study) Investigate the variation of detailed microstructural and mechanical
properties of the Alloy 600 subjected to long-term thermal aging in an operating NPP to evaluate the influence of long-term thermal aging to material property
Approach Thermal aging simulation of light water reactor environment at accelerated temperature
Microstructural analysis with Electron Microscopy Electron Backscattered Diffraction (EBSD)
Mechanical property analysis with Tensile test Nanoindentation
IGSCC resistance analysis with huey test
4
Objective and Approach
Objective and Approach
Alloy 600 thick rod specified by ASTM B166 was provided by Doosan Heavy Industries amp Construction Annealed at 1060 for 35 h and water quenched
Accelerated temperature was determined as 400oC and for activation energy of Cr diffusion at grain boundary 180 kJmol was used for Ni base alloy which containing 15 to 30 wt chromium [1]
5
Experiment (12)
Material amp Thermal aging
Chemical compositions (wt)
Element C Si Mn Cr Cu Ni S Fe
wt 007 033 056 1583 002 7479 lt0001 840
Heat treatment and aging conditions of each specimen Specimen name Simulated aging time and temperature Heat treatment time and temperature
As-received - - HT400_Y10 10 years at 320 1142 hours at 400 HT400_Y20 20 years at 320 2284 hours at 400
119905119886119886119886119886119886119905119903119903119903
= 119890119890119890 minus119876 1
119879119903119903119903minus 1119879119886119886119886119886119886
119877
119905119886119886119886119886119886 119905119903119903119903 119879119886119886119886119886119886 119879119903119903119903
R 119876
= Heat treatment time [h] = Simulated aging time [h] = Heat treatment temperature [K] = Simulated aging temperature [K] = Gas Constance [=8314 JmolK] = Activation Energy for Cr diffusion [kJmol]
Diffusion equation for thermal aging
[1] JM Boursier et al ASME PVP (2004)
6
Experiment (22)
Conditions Experiment conditions
EBSD Acceleration voltage 10 kV Current 064 nA Tilt angle 70deg Step size 2 μm Scanned area 298 μm x 881 μm to cover several number of grains
Nanoindentation Poisson`s ratio 03 Strain rate 005 sec-1
Displacement into surface 2000 nm using berkovich tip To improve the reliability of the results an average was taken from multiple indentations
at random position of matrix Tensile test
Multiple tests were performed at strain rate of 04 sec-1 at room temperature Test were prepared and performed based on ASTM E8-E8m
Huey test 20 cm3 was exposed to 80oC 65 HNO3 solution for 96 hours and weight loss of each
specimens were measured Test were prepared and performed based on ASTM A262
Proportionally reduced specimen from ASTM standard used in tensile test
Specimen As-received HT400_Y10 HT400_Y20
Young`s modulus [GPa] 2113 plusmn 120 2907 plusmn 119 2567 plusmn 464
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
7
Results and discussions (18)
Tensile test
bull At the engineering stress-strain curve hardening occurred by 10 years thermal aging while softening occurred by 20 years thermal aging
Representative stress-strain curves of each specimen
8
Results and discussions (28)
Tensile test
bull At fracture surface of each specimen typical ductile failure mode with many dimple were observed It is hard to quantify the size of dimple since there size is not unique as small dimples observed in large dimples
bull There exist grain boundary fracture in thermally aged specimens
50μm 50μm 50μm
Fracture surface of As-received Fracture surface of HT400_Y10 Fracture surface of HT400_Y20
30μm 30μm 30μm
9
Results and discussions (38)
Hardness
bull In nanoindentation test same trend with tensile test were observed The hardness was increased by 10 years thermal aging and decreased by 20 years thermal aging
bull Hardness at grain boundary have slightly higher value for all specimens however the difference was not significant in order of 005 GPa It is because the plastic deformation zone of indentation is large (~25um) enough to cover several grain boundaries so influence of precipitates to hardness is almost constant
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 247 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 259 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)Indentation depth (nm)
Mean 281 GPa
Nanoindentation result of As-received Nanoindentation result of HT400_Y10 Nanoindentation result of HT400_Y20
Investigated location As-received HT400_Y10 HT400_Y20
Inside grain [GPa] 244 plusmn 003 275 plusmn 008 255 plusmn 009
Cover grain boundary [GPa] 25 plusmn 002 276 plusmn 005 26 plusmn 01
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
30μm 30μm 30μm
10
Results and discussions (48)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
OM image of As-received OM image of HT400_Y10 OM image of HT400_Y20
200μm 200μm 200μm
11
Results and discussions (58)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
30μm 30μm 30μm
10μm 10μm 10μm
bull The morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
12
Results and discussions (68)
Microstructure
bull The morphology of precipitates were known to have significant influence to material`s mechanical properties And this feature is the main reason for mechanical property changes due to thermal aging
bull The feature of calculated material strength according to Orowan mechanism which explain the amount of hardening due to precipiates shows same trend with that of mechanical test which was conducted in this study hardening by 10 years thermal aging and softening by 20 years thermal aging Therefore it could be thought that the aspect of mechanical properties due to thermal aging is closely related to the morphology of precipitates
Material hardening and softening behavior depending on the number fraction and length of precipitates
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates [] 036 plusmn 004 12 plusmn 01 143 plusmn 014
Precipitate length [μm] 080 plusmn 030 092 plusmn 031 186 plusmn 119
Spacing between precipitates [μm] 278 plusmn 022 192 plusmn 014 328 plusmn 031
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
Morphology of precipitates Discrete Semi-continuous Continuous
Summary of mechanical and microstructural characteristics of each specimen
120533 =119918119918
119923 minus 2119955
[1] Z Guo et al Mater Trans (2002) [2] R Hayes et al Acta Metal (1982)
13
Results and discussions (78)
Microstructure Kernel Average Misorientation
Grain boundary misorientation
Grain boundary misorientation
Grain boundary misorientation
Kernel Average Misorientation
Kernel Average Misorientation
EBSD analysis results of HT400_Y20 EBSD analysis results of HT400_Y10 EBSD analysis results of As-received
200μm 200μm 200μm 200μm 200μm 200μm
bull Kernel average misorientation (KAM) which is proportional to residual strain induced by dislocation density was not much changed by thermal aging
bull Grain boundary misorientation however significantly changed Coincidence site lattice boundary which is more resistant to material degradation was decreased by thermal aging The formation of precipitates could be a reason for this however it could be verified with other tools like TEM
14
Results and discussions (88)
Microstructure
bull Major changes induced by thermal aging were length and morphology of precipitates bull HT400_Y10 have semi-continuous precipitates HT400_Y20 have continuous precipitates and As-received
specimen have discontinuous precipitates bull Several previous studies suggest that material with continuous feature of precipitates have lower
susceptibility to SCC than materials with both semi-continuous and discontinuous precipitates bull With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to
formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates []
036 plusmn 004
12 plusmn 01
143 plusmn 014
Precipitate length [μm] 0801 plusmn 0297
0923 plusmn 0312
1864 plusmn 119
Grain size [μm] 2667 2461 2539
Fraction of CSL boundary []
255 plusmn 38
153 plusmn 488
68 plusmn 441
Morphology of precipitates Discrete Semi-
continuous Continuous
Corrosion resistance by huey test [mmyr] 504 697 523
Average properties in electron microscopy
[1] G S Was Corrosion (1990) [2] J R Crum et al 4th EDM-NPS (1990)
SEM images of each specimen (a) as-received (b) HT400_Y10 and (c) HT400_Y20
(a)
(b) (c)
Thermally aged Alloy 600 was investigated to understand the change of microstructural and mechanical features by long-term thermal aging
In tensile and indentation test material shows hardening at 10 years thermal aging while softening happens in 20 years thermal aging This could be explained by Orowan mechanism that there exist peak strength during precipitate strengthening and softening will occur after that point
bull The morphology of precipitates were mainly changed by thermal aging By 10 years thermal aging length was almost same with as-received but area fraction was significantly increased By 20 years thermal aging length was severally increased and area fraction was not much changed And the morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation This will be verified with PWSCC initiation test which will be conducted in PWR environment
15
Summary
Summary
- Slide Number 1
- Slide Number 2
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 10
- Slide Number 11
- Slide Number 12
- Slide Number 13
- Slide Number 14
- Slide Number 15
- Slide Number 16
-
Alloy 600 thick rod specified by ASTM B166 was provided by Doosan Heavy Industries amp Construction Annealed at 1060 for 35 h and water quenched
Accelerated temperature was determined as 400oC and for activation energy of Cr diffusion at grain boundary 180 kJmol was used for Ni base alloy which containing 15 to 30 wt chromium [1]
5
Experiment (12)
Material amp Thermal aging
Chemical compositions (wt)
Element C Si Mn Cr Cu Ni S Fe
wt 007 033 056 1583 002 7479 lt0001 840
Heat treatment and aging conditions of each specimen Specimen name Simulated aging time and temperature Heat treatment time and temperature
As-received - - HT400_Y10 10 years at 320 1142 hours at 400 HT400_Y20 20 years at 320 2284 hours at 400
119905119886119886119886119886119886119905119903119903119903
= 119890119890119890 minus119876 1
119879119903119903119903minus 1119879119886119886119886119886119886
119877
119905119886119886119886119886119886 119905119903119903119903 119879119886119886119886119886119886 119879119903119903119903
R 119876
= Heat treatment time [h] = Simulated aging time [h] = Heat treatment temperature [K] = Simulated aging temperature [K] = Gas Constance [=8314 JmolK] = Activation Energy for Cr diffusion [kJmol]
Diffusion equation for thermal aging
[1] JM Boursier et al ASME PVP (2004)
6
Experiment (22)
Conditions Experiment conditions
EBSD Acceleration voltage 10 kV Current 064 nA Tilt angle 70deg Step size 2 μm Scanned area 298 μm x 881 μm to cover several number of grains
Nanoindentation Poisson`s ratio 03 Strain rate 005 sec-1
Displacement into surface 2000 nm using berkovich tip To improve the reliability of the results an average was taken from multiple indentations
at random position of matrix Tensile test
Multiple tests were performed at strain rate of 04 sec-1 at room temperature Test were prepared and performed based on ASTM E8-E8m
Huey test 20 cm3 was exposed to 80oC 65 HNO3 solution for 96 hours and weight loss of each
specimens were measured Test were prepared and performed based on ASTM A262
Proportionally reduced specimen from ASTM standard used in tensile test
Specimen As-received HT400_Y10 HT400_Y20
Young`s modulus [GPa] 2113 plusmn 120 2907 plusmn 119 2567 plusmn 464
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
7
Results and discussions (18)
Tensile test
bull At the engineering stress-strain curve hardening occurred by 10 years thermal aging while softening occurred by 20 years thermal aging
Representative stress-strain curves of each specimen
8
Results and discussions (28)
Tensile test
bull At fracture surface of each specimen typical ductile failure mode with many dimple were observed It is hard to quantify the size of dimple since there size is not unique as small dimples observed in large dimples
bull There exist grain boundary fracture in thermally aged specimens
50μm 50μm 50μm
Fracture surface of As-received Fracture surface of HT400_Y10 Fracture surface of HT400_Y20
30μm 30μm 30μm
9
Results and discussions (38)
Hardness
bull In nanoindentation test same trend with tensile test were observed The hardness was increased by 10 years thermal aging and decreased by 20 years thermal aging
bull Hardness at grain boundary have slightly higher value for all specimens however the difference was not significant in order of 005 GPa It is because the plastic deformation zone of indentation is large (~25um) enough to cover several grain boundaries so influence of precipitates to hardness is almost constant
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 247 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 259 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)Indentation depth (nm)
Mean 281 GPa
Nanoindentation result of As-received Nanoindentation result of HT400_Y10 Nanoindentation result of HT400_Y20
Investigated location As-received HT400_Y10 HT400_Y20
Inside grain [GPa] 244 plusmn 003 275 plusmn 008 255 plusmn 009
Cover grain boundary [GPa] 25 plusmn 002 276 plusmn 005 26 plusmn 01
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
30μm 30μm 30μm
10
Results and discussions (48)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
OM image of As-received OM image of HT400_Y10 OM image of HT400_Y20
200μm 200μm 200μm
11
Results and discussions (58)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
30μm 30μm 30μm
10μm 10μm 10μm
bull The morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
12
Results and discussions (68)
Microstructure
bull The morphology of precipitates were known to have significant influence to material`s mechanical properties And this feature is the main reason for mechanical property changes due to thermal aging
bull The feature of calculated material strength according to Orowan mechanism which explain the amount of hardening due to precipiates shows same trend with that of mechanical test which was conducted in this study hardening by 10 years thermal aging and softening by 20 years thermal aging Therefore it could be thought that the aspect of mechanical properties due to thermal aging is closely related to the morphology of precipitates
Material hardening and softening behavior depending on the number fraction and length of precipitates
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates [] 036 plusmn 004 12 plusmn 01 143 plusmn 014
Precipitate length [μm] 080 plusmn 030 092 plusmn 031 186 plusmn 119
Spacing between precipitates [μm] 278 plusmn 022 192 plusmn 014 328 plusmn 031
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
Morphology of precipitates Discrete Semi-continuous Continuous
Summary of mechanical and microstructural characteristics of each specimen
120533 =119918119918
119923 minus 2119955
[1] Z Guo et al Mater Trans (2002) [2] R Hayes et al Acta Metal (1982)
13
Results and discussions (78)
Microstructure Kernel Average Misorientation
Grain boundary misorientation
Grain boundary misorientation
Grain boundary misorientation
Kernel Average Misorientation
Kernel Average Misorientation
EBSD analysis results of HT400_Y20 EBSD analysis results of HT400_Y10 EBSD analysis results of As-received
200μm 200μm 200μm 200μm 200μm 200μm
bull Kernel average misorientation (KAM) which is proportional to residual strain induced by dislocation density was not much changed by thermal aging
bull Grain boundary misorientation however significantly changed Coincidence site lattice boundary which is more resistant to material degradation was decreased by thermal aging The formation of precipitates could be a reason for this however it could be verified with other tools like TEM
14
Results and discussions (88)
Microstructure
bull Major changes induced by thermal aging were length and morphology of precipitates bull HT400_Y10 have semi-continuous precipitates HT400_Y20 have continuous precipitates and As-received
specimen have discontinuous precipitates bull Several previous studies suggest that material with continuous feature of precipitates have lower
susceptibility to SCC than materials with both semi-continuous and discontinuous precipitates bull With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to
formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates []
036 plusmn 004
12 plusmn 01
143 plusmn 014
Precipitate length [μm] 0801 plusmn 0297
0923 plusmn 0312
1864 plusmn 119
Grain size [μm] 2667 2461 2539
Fraction of CSL boundary []
255 plusmn 38
153 plusmn 488
68 plusmn 441
Morphology of precipitates Discrete Semi-
continuous Continuous
Corrosion resistance by huey test [mmyr] 504 697 523
Average properties in electron microscopy
[1] G S Was Corrosion (1990) [2] J R Crum et al 4th EDM-NPS (1990)
SEM images of each specimen (a) as-received (b) HT400_Y10 and (c) HT400_Y20
(a)
(b) (c)
Thermally aged Alloy 600 was investigated to understand the change of microstructural and mechanical features by long-term thermal aging
In tensile and indentation test material shows hardening at 10 years thermal aging while softening happens in 20 years thermal aging This could be explained by Orowan mechanism that there exist peak strength during precipitate strengthening and softening will occur after that point
bull The morphology of precipitates were mainly changed by thermal aging By 10 years thermal aging length was almost same with as-received but area fraction was significantly increased By 20 years thermal aging length was severally increased and area fraction was not much changed And the morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation This will be verified with PWSCC initiation test which will be conducted in PWR environment
15
Summary
Summary
- Slide Number 1
- Slide Number 2
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 10
- Slide Number 11
- Slide Number 12
- Slide Number 13
- Slide Number 14
- Slide Number 15
- Slide Number 16
-
6
Experiment (22)
Conditions Experiment conditions
EBSD Acceleration voltage 10 kV Current 064 nA Tilt angle 70deg Step size 2 μm Scanned area 298 μm x 881 μm to cover several number of grains
Nanoindentation Poisson`s ratio 03 Strain rate 005 sec-1
Displacement into surface 2000 nm using berkovich tip To improve the reliability of the results an average was taken from multiple indentations
at random position of matrix Tensile test
Multiple tests were performed at strain rate of 04 sec-1 at room temperature Test were prepared and performed based on ASTM E8-E8m
Huey test 20 cm3 was exposed to 80oC 65 HNO3 solution for 96 hours and weight loss of each
specimens were measured Test were prepared and performed based on ASTM A262
Proportionally reduced specimen from ASTM standard used in tensile test
Specimen As-received HT400_Y10 HT400_Y20
Young`s modulus [GPa] 2113 plusmn 120 2907 plusmn 119 2567 plusmn 464
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
7
Results and discussions (18)
Tensile test
bull At the engineering stress-strain curve hardening occurred by 10 years thermal aging while softening occurred by 20 years thermal aging
Representative stress-strain curves of each specimen
8
Results and discussions (28)
Tensile test
bull At fracture surface of each specimen typical ductile failure mode with many dimple were observed It is hard to quantify the size of dimple since there size is not unique as small dimples observed in large dimples
bull There exist grain boundary fracture in thermally aged specimens
50μm 50μm 50μm
Fracture surface of As-received Fracture surface of HT400_Y10 Fracture surface of HT400_Y20
30μm 30μm 30μm
9
Results and discussions (38)
Hardness
bull In nanoindentation test same trend with tensile test were observed The hardness was increased by 10 years thermal aging and decreased by 20 years thermal aging
bull Hardness at grain boundary have slightly higher value for all specimens however the difference was not significant in order of 005 GPa It is because the plastic deformation zone of indentation is large (~25um) enough to cover several grain boundaries so influence of precipitates to hardness is almost constant
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 247 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 259 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)Indentation depth (nm)
Mean 281 GPa
Nanoindentation result of As-received Nanoindentation result of HT400_Y10 Nanoindentation result of HT400_Y20
Investigated location As-received HT400_Y10 HT400_Y20
Inside grain [GPa] 244 plusmn 003 275 plusmn 008 255 plusmn 009
Cover grain boundary [GPa] 25 plusmn 002 276 plusmn 005 26 plusmn 01
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
30μm 30μm 30μm
10
Results and discussions (48)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
OM image of As-received OM image of HT400_Y10 OM image of HT400_Y20
200μm 200μm 200μm
11
Results and discussions (58)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
30μm 30μm 30μm
10μm 10μm 10μm
bull The morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
12
Results and discussions (68)
Microstructure
bull The morphology of precipitates were known to have significant influence to material`s mechanical properties And this feature is the main reason for mechanical property changes due to thermal aging
bull The feature of calculated material strength according to Orowan mechanism which explain the amount of hardening due to precipiates shows same trend with that of mechanical test which was conducted in this study hardening by 10 years thermal aging and softening by 20 years thermal aging Therefore it could be thought that the aspect of mechanical properties due to thermal aging is closely related to the morphology of precipitates
Material hardening and softening behavior depending on the number fraction and length of precipitates
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates [] 036 plusmn 004 12 plusmn 01 143 plusmn 014
Precipitate length [μm] 080 plusmn 030 092 plusmn 031 186 plusmn 119
Spacing between precipitates [μm] 278 plusmn 022 192 plusmn 014 328 plusmn 031
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
Morphology of precipitates Discrete Semi-continuous Continuous
Summary of mechanical and microstructural characteristics of each specimen
120533 =119918119918
119923 minus 2119955
[1] Z Guo et al Mater Trans (2002) [2] R Hayes et al Acta Metal (1982)
13
Results and discussions (78)
Microstructure Kernel Average Misorientation
Grain boundary misorientation
Grain boundary misorientation
Grain boundary misorientation
Kernel Average Misorientation
Kernel Average Misorientation
EBSD analysis results of HT400_Y20 EBSD analysis results of HT400_Y10 EBSD analysis results of As-received
200μm 200μm 200μm 200μm 200μm 200μm
bull Kernel average misorientation (KAM) which is proportional to residual strain induced by dislocation density was not much changed by thermal aging
bull Grain boundary misorientation however significantly changed Coincidence site lattice boundary which is more resistant to material degradation was decreased by thermal aging The formation of precipitates could be a reason for this however it could be verified with other tools like TEM
14
Results and discussions (88)
Microstructure
bull Major changes induced by thermal aging were length and morphology of precipitates bull HT400_Y10 have semi-continuous precipitates HT400_Y20 have continuous precipitates and As-received
specimen have discontinuous precipitates bull Several previous studies suggest that material with continuous feature of precipitates have lower
susceptibility to SCC than materials with both semi-continuous and discontinuous precipitates bull With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to
formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates []
036 plusmn 004
12 plusmn 01
143 plusmn 014
Precipitate length [μm] 0801 plusmn 0297
0923 plusmn 0312
1864 plusmn 119
Grain size [μm] 2667 2461 2539
Fraction of CSL boundary []
255 plusmn 38
153 plusmn 488
68 plusmn 441
Morphology of precipitates Discrete Semi-
continuous Continuous
Corrosion resistance by huey test [mmyr] 504 697 523
Average properties in electron microscopy
[1] G S Was Corrosion (1990) [2] J R Crum et al 4th EDM-NPS (1990)
SEM images of each specimen (a) as-received (b) HT400_Y10 and (c) HT400_Y20
(a)
(b) (c)
Thermally aged Alloy 600 was investigated to understand the change of microstructural and mechanical features by long-term thermal aging
In tensile and indentation test material shows hardening at 10 years thermal aging while softening happens in 20 years thermal aging This could be explained by Orowan mechanism that there exist peak strength during precipitate strengthening and softening will occur after that point
bull The morphology of precipitates were mainly changed by thermal aging By 10 years thermal aging length was almost same with as-received but area fraction was significantly increased By 20 years thermal aging length was severally increased and area fraction was not much changed And the morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation This will be verified with PWSCC initiation test which will be conducted in PWR environment
15
Summary
Summary
- Slide Number 1
- Slide Number 2
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 10
- Slide Number 11
- Slide Number 12
- Slide Number 13
- Slide Number 14
- Slide Number 15
- Slide Number 16
-
Specimen As-received HT400_Y10 HT400_Y20
Young`s modulus [GPa] 2113 plusmn 120 2907 plusmn 119 2567 plusmn 464
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
7
Results and discussions (18)
Tensile test
bull At the engineering stress-strain curve hardening occurred by 10 years thermal aging while softening occurred by 20 years thermal aging
Representative stress-strain curves of each specimen
8
Results and discussions (28)
Tensile test
bull At fracture surface of each specimen typical ductile failure mode with many dimple were observed It is hard to quantify the size of dimple since there size is not unique as small dimples observed in large dimples
bull There exist grain boundary fracture in thermally aged specimens
50μm 50μm 50μm
Fracture surface of As-received Fracture surface of HT400_Y10 Fracture surface of HT400_Y20
30μm 30μm 30μm
9
Results and discussions (38)
Hardness
bull In nanoindentation test same trend with tensile test were observed The hardness was increased by 10 years thermal aging and decreased by 20 years thermal aging
bull Hardness at grain boundary have slightly higher value for all specimens however the difference was not significant in order of 005 GPa It is because the plastic deformation zone of indentation is large (~25um) enough to cover several grain boundaries so influence of precipitates to hardness is almost constant
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 247 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 259 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)Indentation depth (nm)
Mean 281 GPa
Nanoindentation result of As-received Nanoindentation result of HT400_Y10 Nanoindentation result of HT400_Y20
Investigated location As-received HT400_Y10 HT400_Y20
Inside grain [GPa] 244 plusmn 003 275 plusmn 008 255 plusmn 009
Cover grain boundary [GPa] 25 plusmn 002 276 plusmn 005 26 plusmn 01
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
30μm 30μm 30μm
10
Results and discussions (48)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
OM image of As-received OM image of HT400_Y10 OM image of HT400_Y20
200μm 200μm 200μm
11
Results and discussions (58)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
30μm 30μm 30μm
10μm 10μm 10μm
bull The morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
12
Results and discussions (68)
Microstructure
bull The morphology of precipitates were known to have significant influence to material`s mechanical properties And this feature is the main reason for mechanical property changes due to thermal aging
bull The feature of calculated material strength according to Orowan mechanism which explain the amount of hardening due to precipiates shows same trend with that of mechanical test which was conducted in this study hardening by 10 years thermal aging and softening by 20 years thermal aging Therefore it could be thought that the aspect of mechanical properties due to thermal aging is closely related to the morphology of precipitates
Material hardening and softening behavior depending on the number fraction and length of precipitates
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates [] 036 plusmn 004 12 plusmn 01 143 plusmn 014
Precipitate length [μm] 080 plusmn 030 092 plusmn 031 186 plusmn 119
Spacing between precipitates [μm] 278 plusmn 022 192 plusmn 014 328 plusmn 031
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
Morphology of precipitates Discrete Semi-continuous Continuous
Summary of mechanical and microstructural characteristics of each specimen
120533 =119918119918
119923 minus 2119955
[1] Z Guo et al Mater Trans (2002) [2] R Hayes et al Acta Metal (1982)
13
Results and discussions (78)
Microstructure Kernel Average Misorientation
Grain boundary misorientation
Grain boundary misorientation
Grain boundary misorientation
Kernel Average Misorientation
Kernel Average Misorientation
EBSD analysis results of HT400_Y20 EBSD analysis results of HT400_Y10 EBSD analysis results of As-received
200μm 200μm 200μm 200μm 200μm 200μm
bull Kernel average misorientation (KAM) which is proportional to residual strain induced by dislocation density was not much changed by thermal aging
bull Grain boundary misorientation however significantly changed Coincidence site lattice boundary which is more resistant to material degradation was decreased by thermal aging The formation of precipitates could be a reason for this however it could be verified with other tools like TEM
14
Results and discussions (88)
Microstructure
bull Major changes induced by thermal aging were length and morphology of precipitates bull HT400_Y10 have semi-continuous precipitates HT400_Y20 have continuous precipitates and As-received
specimen have discontinuous precipitates bull Several previous studies suggest that material with continuous feature of precipitates have lower
susceptibility to SCC than materials with both semi-continuous and discontinuous precipitates bull With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to
formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates []
036 plusmn 004
12 plusmn 01
143 plusmn 014
Precipitate length [μm] 0801 plusmn 0297
0923 plusmn 0312
1864 plusmn 119
Grain size [μm] 2667 2461 2539
Fraction of CSL boundary []
255 plusmn 38
153 plusmn 488
68 plusmn 441
Morphology of precipitates Discrete Semi-
continuous Continuous
Corrosion resistance by huey test [mmyr] 504 697 523
Average properties in electron microscopy
[1] G S Was Corrosion (1990) [2] J R Crum et al 4th EDM-NPS (1990)
SEM images of each specimen (a) as-received (b) HT400_Y10 and (c) HT400_Y20
(a)
(b) (c)
Thermally aged Alloy 600 was investigated to understand the change of microstructural and mechanical features by long-term thermal aging
In tensile and indentation test material shows hardening at 10 years thermal aging while softening happens in 20 years thermal aging This could be explained by Orowan mechanism that there exist peak strength during precipitate strengthening and softening will occur after that point
bull The morphology of precipitates were mainly changed by thermal aging By 10 years thermal aging length was almost same with as-received but area fraction was significantly increased By 20 years thermal aging length was severally increased and area fraction was not much changed And the morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation This will be verified with PWSCC initiation test which will be conducted in PWR environment
15
Summary
Summary
- Slide Number 1
- Slide Number 2
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 10
- Slide Number 11
- Slide Number 12
- Slide Number 13
- Slide Number 14
- Slide Number 15
- Slide Number 16
-
8
Results and discussions (28)
Tensile test
bull At fracture surface of each specimen typical ductile failure mode with many dimple were observed It is hard to quantify the size of dimple since there size is not unique as small dimples observed in large dimples
bull There exist grain boundary fracture in thermally aged specimens
50μm 50μm 50μm
Fracture surface of As-received Fracture surface of HT400_Y10 Fracture surface of HT400_Y20
30μm 30μm 30μm
9
Results and discussions (38)
Hardness
bull In nanoindentation test same trend with tensile test were observed The hardness was increased by 10 years thermal aging and decreased by 20 years thermal aging
bull Hardness at grain boundary have slightly higher value for all specimens however the difference was not significant in order of 005 GPa It is because the plastic deformation zone of indentation is large (~25um) enough to cover several grain boundaries so influence of precipitates to hardness is almost constant
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 247 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 259 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)Indentation depth (nm)
Mean 281 GPa
Nanoindentation result of As-received Nanoindentation result of HT400_Y10 Nanoindentation result of HT400_Y20
Investigated location As-received HT400_Y10 HT400_Y20
Inside grain [GPa] 244 plusmn 003 275 plusmn 008 255 plusmn 009
Cover grain boundary [GPa] 25 plusmn 002 276 plusmn 005 26 plusmn 01
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
30μm 30μm 30μm
10
Results and discussions (48)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
OM image of As-received OM image of HT400_Y10 OM image of HT400_Y20
200μm 200μm 200μm
11
Results and discussions (58)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
30μm 30μm 30μm
10μm 10μm 10μm
bull The morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
12
Results and discussions (68)
Microstructure
bull The morphology of precipitates were known to have significant influence to material`s mechanical properties And this feature is the main reason for mechanical property changes due to thermal aging
bull The feature of calculated material strength according to Orowan mechanism which explain the amount of hardening due to precipiates shows same trend with that of mechanical test which was conducted in this study hardening by 10 years thermal aging and softening by 20 years thermal aging Therefore it could be thought that the aspect of mechanical properties due to thermal aging is closely related to the morphology of precipitates
Material hardening and softening behavior depending on the number fraction and length of precipitates
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates [] 036 plusmn 004 12 plusmn 01 143 plusmn 014
Precipitate length [μm] 080 plusmn 030 092 plusmn 031 186 plusmn 119
Spacing between precipitates [μm] 278 plusmn 022 192 plusmn 014 328 plusmn 031
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
Morphology of precipitates Discrete Semi-continuous Continuous
Summary of mechanical and microstructural characteristics of each specimen
120533 =119918119918
119923 minus 2119955
[1] Z Guo et al Mater Trans (2002) [2] R Hayes et al Acta Metal (1982)
13
Results and discussions (78)
Microstructure Kernel Average Misorientation
Grain boundary misorientation
Grain boundary misorientation
Grain boundary misorientation
Kernel Average Misorientation
Kernel Average Misorientation
EBSD analysis results of HT400_Y20 EBSD analysis results of HT400_Y10 EBSD analysis results of As-received
200μm 200μm 200μm 200μm 200μm 200μm
bull Kernel average misorientation (KAM) which is proportional to residual strain induced by dislocation density was not much changed by thermal aging
bull Grain boundary misorientation however significantly changed Coincidence site lattice boundary which is more resistant to material degradation was decreased by thermal aging The formation of precipitates could be a reason for this however it could be verified with other tools like TEM
14
Results and discussions (88)
Microstructure
bull Major changes induced by thermal aging were length and morphology of precipitates bull HT400_Y10 have semi-continuous precipitates HT400_Y20 have continuous precipitates and As-received
specimen have discontinuous precipitates bull Several previous studies suggest that material with continuous feature of precipitates have lower
susceptibility to SCC than materials with both semi-continuous and discontinuous precipitates bull With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to
formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates []
036 plusmn 004
12 plusmn 01
143 plusmn 014
Precipitate length [μm] 0801 plusmn 0297
0923 plusmn 0312
1864 plusmn 119
Grain size [μm] 2667 2461 2539
Fraction of CSL boundary []
255 plusmn 38
153 plusmn 488
68 plusmn 441
Morphology of precipitates Discrete Semi-
continuous Continuous
Corrosion resistance by huey test [mmyr] 504 697 523
Average properties in electron microscopy
[1] G S Was Corrosion (1990) [2] J R Crum et al 4th EDM-NPS (1990)
SEM images of each specimen (a) as-received (b) HT400_Y10 and (c) HT400_Y20
(a)
(b) (c)
Thermally aged Alloy 600 was investigated to understand the change of microstructural and mechanical features by long-term thermal aging
In tensile and indentation test material shows hardening at 10 years thermal aging while softening happens in 20 years thermal aging This could be explained by Orowan mechanism that there exist peak strength during precipitate strengthening and softening will occur after that point
bull The morphology of precipitates were mainly changed by thermal aging By 10 years thermal aging length was almost same with as-received but area fraction was significantly increased By 20 years thermal aging length was severally increased and area fraction was not much changed And the morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation This will be verified with PWSCC initiation test which will be conducted in PWR environment
15
Summary
Summary
- Slide Number 1
- Slide Number 2
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 10
- Slide Number 11
- Slide Number 12
- Slide Number 13
- Slide Number 14
- Slide Number 15
- Slide Number 16
-
9
Results and discussions (38)
Hardness
bull In nanoindentation test same trend with tensile test were observed The hardness was increased by 10 years thermal aging and decreased by 20 years thermal aging
bull Hardness at grain boundary have slightly higher value for all specimens however the difference was not significant in order of 005 GPa It is because the plastic deformation zone of indentation is large (~25um) enough to cover several grain boundaries so influence of precipitates to hardness is almost constant
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 247 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)
Indentation depth (nm)
Mean 259 GPa
0 500 1000 1500 20000
2
4
6
8
10
Hard
ness
(GPa
)Indentation depth (nm)
Mean 281 GPa
Nanoindentation result of As-received Nanoindentation result of HT400_Y10 Nanoindentation result of HT400_Y20
Investigated location As-received HT400_Y10 HT400_Y20
Inside grain [GPa] 244 plusmn 003 275 plusmn 008 255 plusmn 009
Cover grain boundary [GPa] 25 plusmn 002 276 plusmn 005 26 plusmn 01
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
30μm 30μm 30μm
10
Results and discussions (48)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
OM image of As-received OM image of HT400_Y10 OM image of HT400_Y20
200μm 200μm 200μm
11
Results and discussions (58)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
30μm 30μm 30μm
10μm 10μm 10μm
bull The morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
12
Results and discussions (68)
Microstructure
bull The morphology of precipitates were known to have significant influence to material`s mechanical properties And this feature is the main reason for mechanical property changes due to thermal aging
bull The feature of calculated material strength according to Orowan mechanism which explain the amount of hardening due to precipiates shows same trend with that of mechanical test which was conducted in this study hardening by 10 years thermal aging and softening by 20 years thermal aging Therefore it could be thought that the aspect of mechanical properties due to thermal aging is closely related to the morphology of precipitates
Material hardening and softening behavior depending on the number fraction and length of precipitates
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates [] 036 plusmn 004 12 plusmn 01 143 plusmn 014
Precipitate length [μm] 080 plusmn 030 092 plusmn 031 186 plusmn 119
Spacing between precipitates [μm] 278 plusmn 022 192 plusmn 014 328 plusmn 031
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
Morphology of precipitates Discrete Semi-continuous Continuous
Summary of mechanical and microstructural characteristics of each specimen
120533 =119918119918
119923 minus 2119955
[1] Z Guo et al Mater Trans (2002) [2] R Hayes et al Acta Metal (1982)
13
Results and discussions (78)
Microstructure Kernel Average Misorientation
Grain boundary misorientation
Grain boundary misorientation
Grain boundary misorientation
Kernel Average Misorientation
Kernel Average Misorientation
EBSD analysis results of HT400_Y20 EBSD analysis results of HT400_Y10 EBSD analysis results of As-received
200μm 200μm 200μm 200μm 200μm 200μm
bull Kernel average misorientation (KAM) which is proportional to residual strain induced by dislocation density was not much changed by thermal aging
bull Grain boundary misorientation however significantly changed Coincidence site lattice boundary which is more resistant to material degradation was decreased by thermal aging The formation of precipitates could be a reason for this however it could be verified with other tools like TEM
14
Results and discussions (88)
Microstructure
bull Major changes induced by thermal aging were length and morphology of precipitates bull HT400_Y10 have semi-continuous precipitates HT400_Y20 have continuous precipitates and As-received
specimen have discontinuous precipitates bull Several previous studies suggest that material with continuous feature of precipitates have lower
susceptibility to SCC than materials with both semi-continuous and discontinuous precipitates bull With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to
formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates []
036 plusmn 004
12 plusmn 01
143 plusmn 014
Precipitate length [μm] 0801 plusmn 0297
0923 plusmn 0312
1864 plusmn 119
Grain size [μm] 2667 2461 2539
Fraction of CSL boundary []
255 plusmn 38
153 plusmn 488
68 plusmn 441
Morphology of precipitates Discrete Semi-
continuous Continuous
Corrosion resistance by huey test [mmyr] 504 697 523
Average properties in electron microscopy
[1] G S Was Corrosion (1990) [2] J R Crum et al 4th EDM-NPS (1990)
SEM images of each specimen (a) as-received (b) HT400_Y10 and (c) HT400_Y20
(a)
(b) (c)
Thermally aged Alloy 600 was investigated to understand the change of microstructural and mechanical features by long-term thermal aging
In tensile and indentation test material shows hardening at 10 years thermal aging while softening happens in 20 years thermal aging This could be explained by Orowan mechanism that there exist peak strength during precipitate strengthening and softening will occur after that point
bull The morphology of precipitates were mainly changed by thermal aging By 10 years thermal aging length was almost same with as-received but area fraction was significantly increased By 20 years thermal aging length was severally increased and area fraction was not much changed And the morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation This will be verified with PWSCC initiation test which will be conducted in PWR environment
15
Summary
Summary
- Slide Number 1
- Slide Number 2
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 10
- Slide Number 11
- Slide Number 12
- Slide Number 13
- Slide Number 14
- Slide Number 15
- Slide Number 16
-
30μm 30μm 30μm
10
Results and discussions (48)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
OM image of As-received OM image of HT400_Y10 OM image of HT400_Y20
200μm 200μm 200μm
11
Results and discussions (58)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
30μm 30μm 30μm
10μm 10μm 10μm
bull The morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
12
Results and discussions (68)
Microstructure
bull The morphology of precipitates were known to have significant influence to material`s mechanical properties And this feature is the main reason for mechanical property changes due to thermal aging
bull The feature of calculated material strength according to Orowan mechanism which explain the amount of hardening due to precipiates shows same trend with that of mechanical test which was conducted in this study hardening by 10 years thermal aging and softening by 20 years thermal aging Therefore it could be thought that the aspect of mechanical properties due to thermal aging is closely related to the morphology of precipitates
Material hardening and softening behavior depending on the number fraction and length of precipitates
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates [] 036 plusmn 004 12 plusmn 01 143 plusmn 014
Precipitate length [μm] 080 plusmn 030 092 plusmn 031 186 plusmn 119
Spacing between precipitates [μm] 278 plusmn 022 192 plusmn 014 328 plusmn 031
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
Morphology of precipitates Discrete Semi-continuous Continuous
Summary of mechanical and microstructural characteristics of each specimen
120533 =119918119918
119923 minus 2119955
[1] Z Guo et al Mater Trans (2002) [2] R Hayes et al Acta Metal (1982)
13
Results and discussions (78)
Microstructure Kernel Average Misorientation
Grain boundary misorientation
Grain boundary misorientation
Grain boundary misorientation
Kernel Average Misorientation
Kernel Average Misorientation
EBSD analysis results of HT400_Y20 EBSD analysis results of HT400_Y10 EBSD analysis results of As-received
200μm 200μm 200μm 200μm 200μm 200μm
bull Kernel average misorientation (KAM) which is proportional to residual strain induced by dislocation density was not much changed by thermal aging
bull Grain boundary misorientation however significantly changed Coincidence site lattice boundary which is more resistant to material degradation was decreased by thermal aging The formation of precipitates could be a reason for this however it could be verified with other tools like TEM
14
Results and discussions (88)
Microstructure
bull Major changes induced by thermal aging were length and morphology of precipitates bull HT400_Y10 have semi-continuous precipitates HT400_Y20 have continuous precipitates and As-received
specimen have discontinuous precipitates bull Several previous studies suggest that material with continuous feature of precipitates have lower
susceptibility to SCC than materials with both semi-continuous and discontinuous precipitates bull With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to
formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates []
036 plusmn 004
12 plusmn 01
143 plusmn 014
Precipitate length [μm] 0801 plusmn 0297
0923 plusmn 0312
1864 plusmn 119
Grain size [μm] 2667 2461 2539
Fraction of CSL boundary []
255 plusmn 38
153 plusmn 488
68 plusmn 441
Morphology of precipitates Discrete Semi-
continuous Continuous
Corrosion resistance by huey test [mmyr] 504 697 523
Average properties in electron microscopy
[1] G S Was Corrosion (1990) [2] J R Crum et al 4th EDM-NPS (1990)
SEM images of each specimen (a) as-received (b) HT400_Y10 and (c) HT400_Y20
(a)
(b) (c)
Thermally aged Alloy 600 was investigated to understand the change of microstructural and mechanical features by long-term thermal aging
In tensile and indentation test material shows hardening at 10 years thermal aging while softening happens in 20 years thermal aging This could be explained by Orowan mechanism that there exist peak strength during precipitate strengthening and softening will occur after that point
bull The morphology of precipitates were mainly changed by thermal aging By 10 years thermal aging length was almost same with as-received but area fraction was significantly increased By 20 years thermal aging length was severally increased and area fraction was not much changed And the morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation This will be verified with PWSCC initiation test which will be conducted in PWR environment
15
Summary
Summary
- Slide Number 1
- Slide Number 2
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 10
- Slide Number 11
- Slide Number 12
- Slide Number 13
- Slide Number 14
- Slide Number 15
- Slide Number 16
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11
Results and discussions (58)
Microstructure
SEM image of HT400_Y20 SEM image of HT400_Y10 SEM image of As-received
30μm 30μm 30μm
10μm 10μm 10μm
bull The morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
12
Results and discussions (68)
Microstructure
bull The morphology of precipitates were known to have significant influence to material`s mechanical properties And this feature is the main reason for mechanical property changes due to thermal aging
bull The feature of calculated material strength according to Orowan mechanism which explain the amount of hardening due to precipiates shows same trend with that of mechanical test which was conducted in this study hardening by 10 years thermal aging and softening by 20 years thermal aging Therefore it could be thought that the aspect of mechanical properties due to thermal aging is closely related to the morphology of precipitates
Material hardening and softening behavior depending on the number fraction and length of precipitates
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates [] 036 plusmn 004 12 plusmn 01 143 plusmn 014
Precipitate length [μm] 080 plusmn 030 092 plusmn 031 186 plusmn 119
Spacing between precipitates [μm] 278 plusmn 022 192 plusmn 014 328 plusmn 031
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
Morphology of precipitates Discrete Semi-continuous Continuous
Summary of mechanical and microstructural characteristics of each specimen
120533 =119918119918
119923 minus 2119955
[1] Z Guo et al Mater Trans (2002) [2] R Hayes et al Acta Metal (1982)
13
Results and discussions (78)
Microstructure Kernel Average Misorientation
Grain boundary misorientation
Grain boundary misorientation
Grain boundary misorientation
Kernel Average Misorientation
Kernel Average Misorientation
EBSD analysis results of HT400_Y20 EBSD analysis results of HT400_Y10 EBSD analysis results of As-received
200μm 200μm 200μm 200μm 200μm 200μm
bull Kernel average misorientation (KAM) which is proportional to residual strain induced by dislocation density was not much changed by thermal aging
bull Grain boundary misorientation however significantly changed Coincidence site lattice boundary which is more resistant to material degradation was decreased by thermal aging The formation of precipitates could be a reason for this however it could be verified with other tools like TEM
14
Results and discussions (88)
Microstructure
bull Major changes induced by thermal aging were length and morphology of precipitates bull HT400_Y10 have semi-continuous precipitates HT400_Y20 have continuous precipitates and As-received
specimen have discontinuous precipitates bull Several previous studies suggest that material with continuous feature of precipitates have lower
susceptibility to SCC than materials with both semi-continuous and discontinuous precipitates bull With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to
formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates []
036 plusmn 004
12 plusmn 01
143 plusmn 014
Precipitate length [μm] 0801 plusmn 0297
0923 plusmn 0312
1864 plusmn 119
Grain size [μm] 2667 2461 2539
Fraction of CSL boundary []
255 plusmn 38
153 plusmn 488
68 plusmn 441
Morphology of precipitates Discrete Semi-
continuous Continuous
Corrosion resistance by huey test [mmyr] 504 697 523
Average properties in electron microscopy
[1] G S Was Corrosion (1990) [2] J R Crum et al 4th EDM-NPS (1990)
SEM images of each specimen (a) as-received (b) HT400_Y10 and (c) HT400_Y20
(a)
(b) (c)
Thermally aged Alloy 600 was investigated to understand the change of microstructural and mechanical features by long-term thermal aging
In tensile and indentation test material shows hardening at 10 years thermal aging while softening happens in 20 years thermal aging This could be explained by Orowan mechanism that there exist peak strength during precipitate strengthening and softening will occur after that point
bull The morphology of precipitates were mainly changed by thermal aging By 10 years thermal aging length was almost same with as-received but area fraction was significantly increased By 20 years thermal aging length was severally increased and area fraction was not much changed And the morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation This will be verified with PWSCC initiation test which will be conducted in PWR environment
15
Summary
Summary
- Slide Number 1
- Slide Number 2
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 10
- Slide Number 11
- Slide Number 12
- Slide Number 13
- Slide Number 14
- Slide Number 15
- Slide Number 16
-
12
Results and discussions (68)
Microstructure
bull The morphology of precipitates were known to have significant influence to material`s mechanical properties And this feature is the main reason for mechanical property changes due to thermal aging
bull The feature of calculated material strength according to Orowan mechanism which explain the amount of hardening due to precipiates shows same trend with that of mechanical test which was conducted in this study hardening by 10 years thermal aging and softening by 20 years thermal aging Therefore it could be thought that the aspect of mechanical properties due to thermal aging is closely related to the morphology of precipitates
Material hardening and softening behavior depending on the number fraction and length of precipitates
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates [] 036 plusmn 004 12 plusmn 01 143 plusmn 014
Precipitate length [μm] 080 plusmn 030 092 plusmn 031 186 plusmn 119
Spacing between precipitates [μm] 278 plusmn 022 192 plusmn 014 328 plusmn 031
Average hardness [GPa] 247 plusmn 014 281 plusmn 024 259 plusmn 031
02 offset yield strength [MPa] 4095 plusmn 109 5873 plusmn 59 4973 plusmn 22
Ultimate tensile strength [MPa] 7018 plusmn 245 7757 plusmn 247 7677 plusmn 25
Elongation [] 500 plusmn 16 360 plusmn 16 420 plusmn 31
Morphology of precipitates Discrete Semi-continuous Continuous
Summary of mechanical and microstructural characteristics of each specimen
120533 =119918119918
119923 minus 2119955
[1] Z Guo et al Mater Trans (2002) [2] R Hayes et al Acta Metal (1982)
13
Results and discussions (78)
Microstructure Kernel Average Misorientation
Grain boundary misorientation
Grain boundary misorientation
Grain boundary misorientation
Kernel Average Misorientation
Kernel Average Misorientation
EBSD analysis results of HT400_Y20 EBSD analysis results of HT400_Y10 EBSD analysis results of As-received
200μm 200μm 200μm 200μm 200μm 200μm
bull Kernel average misorientation (KAM) which is proportional to residual strain induced by dislocation density was not much changed by thermal aging
bull Grain boundary misorientation however significantly changed Coincidence site lattice boundary which is more resistant to material degradation was decreased by thermal aging The formation of precipitates could be a reason for this however it could be verified with other tools like TEM
14
Results and discussions (88)
Microstructure
bull Major changes induced by thermal aging were length and morphology of precipitates bull HT400_Y10 have semi-continuous precipitates HT400_Y20 have continuous precipitates and As-received
specimen have discontinuous precipitates bull Several previous studies suggest that material with continuous feature of precipitates have lower
susceptibility to SCC than materials with both semi-continuous and discontinuous precipitates bull With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to
formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates []
036 plusmn 004
12 plusmn 01
143 plusmn 014
Precipitate length [μm] 0801 plusmn 0297
0923 plusmn 0312
1864 plusmn 119
Grain size [μm] 2667 2461 2539
Fraction of CSL boundary []
255 plusmn 38
153 plusmn 488
68 plusmn 441
Morphology of precipitates Discrete Semi-
continuous Continuous
Corrosion resistance by huey test [mmyr] 504 697 523
Average properties in electron microscopy
[1] G S Was Corrosion (1990) [2] J R Crum et al 4th EDM-NPS (1990)
SEM images of each specimen (a) as-received (b) HT400_Y10 and (c) HT400_Y20
(a)
(b) (c)
Thermally aged Alloy 600 was investigated to understand the change of microstructural and mechanical features by long-term thermal aging
In tensile and indentation test material shows hardening at 10 years thermal aging while softening happens in 20 years thermal aging This could be explained by Orowan mechanism that there exist peak strength during precipitate strengthening and softening will occur after that point
bull The morphology of precipitates were mainly changed by thermal aging By 10 years thermal aging length was almost same with as-received but area fraction was significantly increased By 20 years thermal aging length was severally increased and area fraction was not much changed And the morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation This will be verified with PWSCC initiation test which will be conducted in PWR environment
15
Summary
Summary
- Slide Number 1
- Slide Number 2
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 10
- Slide Number 11
- Slide Number 12
- Slide Number 13
- Slide Number 14
- Slide Number 15
- Slide Number 16
-
13
Results and discussions (78)
Microstructure Kernel Average Misorientation
Grain boundary misorientation
Grain boundary misorientation
Grain boundary misorientation
Kernel Average Misorientation
Kernel Average Misorientation
EBSD analysis results of HT400_Y20 EBSD analysis results of HT400_Y10 EBSD analysis results of As-received
200μm 200μm 200μm 200μm 200μm 200μm
bull Kernel average misorientation (KAM) which is proportional to residual strain induced by dislocation density was not much changed by thermal aging
bull Grain boundary misorientation however significantly changed Coincidence site lattice boundary which is more resistant to material degradation was decreased by thermal aging The formation of precipitates could be a reason for this however it could be verified with other tools like TEM
14
Results and discussions (88)
Microstructure
bull Major changes induced by thermal aging were length and morphology of precipitates bull HT400_Y10 have semi-continuous precipitates HT400_Y20 have continuous precipitates and As-received
specimen have discontinuous precipitates bull Several previous studies suggest that material with continuous feature of precipitates have lower
susceptibility to SCC than materials with both semi-continuous and discontinuous precipitates bull With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to
formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates []
036 plusmn 004
12 plusmn 01
143 plusmn 014
Precipitate length [μm] 0801 plusmn 0297
0923 plusmn 0312
1864 plusmn 119
Grain size [μm] 2667 2461 2539
Fraction of CSL boundary []
255 plusmn 38
153 plusmn 488
68 plusmn 441
Morphology of precipitates Discrete Semi-
continuous Continuous
Corrosion resistance by huey test [mmyr] 504 697 523
Average properties in electron microscopy
[1] G S Was Corrosion (1990) [2] J R Crum et al 4th EDM-NPS (1990)
SEM images of each specimen (a) as-received (b) HT400_Y10 and (c) HT400_Y20
(a)
(b) (c)
Thermally aged Alloy 600 was investigated to understand the change of microstructural and mechanical features by long-term thermal aging
In tensile and indentation test material shows hardening at 10 years thermal aging while softening happens in 20 years thermal aging This could be explained by Orowan mechanism that there exist peak strength during precipitate strengthening and softening will occur after that point
bull The morphology of precipitates were mainly changed by thermal aging By 10 years thermal aging length was almost same with as-received but area fraction was significantly increased By 20 years thermal aging length was severally increased and area fraction was not much changed And the morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation This will be verified with PWSCC initiation test which will be conducted in PWR environment
15
Summary
Summary
- Slide Number 1
- Slide Number 2
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 10
- Slide Number 11
- Slide Number 12
- Slide Number 13
- Slide Number 14
- Slide Number 15
- Slide Number 16
-
14
Results and discussions (88)
Microstructure
bull Major changes induced by thermal aging were length and morphology of precipitates bull HT400_Y10 have semi-continuous precipitates HT400_Y20 have continuous precipitates and As-received
specimen have discontinuous precipitates bull Several previous studies suggest that material with continuous feature of precipitates have lower
susceptibility to SCC than materials with both semi-continuous and discontinuous precipitates bull With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to
formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation
Specimen As-received HT400_Y10 HT400_Y20
Area fraction of precipitates []
036 plusmn 004
12 plusmn 01
143 plusmn 014
Precipitate length [μm] 0801 plusmn 0297
0923 plusmn 0312
1864 plusmn 119
Grain size [μm] 2667 2461 2539
Fraction of CSL boundary []
255 plusmn 38
153 plusmn 488
68 plusmn 441
Morphology of precipitates Discrete Semi-
continuous Continuous
Corrosion resistance by huey test [mmyr] 504 697 523
Average properties in electron microscopy
[1] G S Was Corrosion (1990) [2] J R Crum et al 4th EDM-NPS (1990)
SEM images of each specimen (a) as-received (b) HT400_Y10 and (c) HT400_Y20
(a)
(b) (c)
Thermally aged Alloy 600 was investigated to understand the change of microstructural and mechanical features by long-term thermal aging
In tensile and indentation test material shows hardening at 10 years thermal aging while softening happens in 20 years thermal aging This could be explained by Orowan mechanism that there exist peak strength during precipitate strengthening and softening will occur after that point
bull The morphology of precipitates were mainly changed by thermal aging By 10 years thermal aging length was almost same with as-received but area fraction was significantly increased By 20 years thermal aging length was severally increased and area fraction was not much changed And the morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation This will be verified with PWSCC initiation test which will be conducted in PWR environment
15
Summary
Summary
- Slide Number 1
- Slide Number 2
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 10
- Slide Number 11
- Slide Number 12
- Slide Number 13
- Slide Number 14
- Slide Number 15
- Slide Number 16
-
Thermally aged Alloy 600 was investigated to understand the change of microstructural and mechanical features by long-term thermal aging
In tensile and indentation test material shows hardening at 10 years thermal aging while softening happens in 20 years thermal aging This could be explained by Orowan mechanism that there exist peak strength during precipitate strengthening and softening will occur after that point
bull The morphology of precipitates were mainly changed by thermal aging By 10 years thermal aging length was almost same with as-received but area fraction was significantly increased By 20 years thermal aging length was severally increased and area fraction was not much changed And the morphology of precipitates were discrete at as-received specimen while it was semi-continuous for 10 years thermal aging and continuous for 20 years thermal aging
With consideration of corrosion resistance influenced by chromium depletion at grain boundary due to formation of precipitates it is expected that HT400_Y10 which have large amount of semi-continuous precipitates and have high susceptibility to corrosion would have higher susceptibility to SCC initiation This will be verified with PWSCC initiation test which will be conducted in PWR environment
15
Summary
Summary
- Slide Number 1
- Slide Number 2
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 10
- Slide Number 11
- Slide Number 12
- Slide Number 13
- Slide Number 14
- Slide Number 15
- Slide Number 16
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- Slide Number 1
- Slide Number 2
- Slide Number 3
- Slide Number 4
- Slide Number 5
- Slide Number 6
- Slide Number 7
- Slide Number 8
- Slide Number 9
- Slide Number 10
- Slide Number 11
- Slide Number 12
- Slide Number 13
- Slide Number 14
- Slide Number 15
- Slide Number 16
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