crrep high temp
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MKM6144ADVANCED MATERIAL
FACULTY OF MECHANICAL ENGINEERING
UNIVERSITI MALAYSIA PAHANG
IntroductionSubject : ADVANCED MATERIALCourse Code : MKM6144Credits : 4 CreditsSemester : 2 2015/2016Team Teaching : Dr. YULI PANCA ASMARA Dr. TEDI KURNIAWAN Dr. DANDI BACHTIAR Dr. JANUAR PARLAUNGAN SIREGAR
Oxidation and Corrosion inHigh-Temperature Systems
Course Description
Materials used for high temperature applications are subjected to various types of degradation phenomenon such as high temperature corrosion, erosion-corrosion, overheating, solid particle abrasion, wear, etc. Boiler tubes used for super-heaters and re-heaters in steam-generating systems are subjected to erosion-corrosion at high temperature, resulting in tube wall thinning and premature failure. The present study investigates the high temperature erosion-corrosion resistance of D-gun sprayed coatings on “ASTM-SA210-GradeA1” boiler tube steel in actual industrial environment. SEM/EDAX, XRD and X-ray mapping analysis is done to reveal the microstructural and compositional features of coated boiler tube steel. The deposited coatings on Grade A1 steel exhibit uniform and dense microstructure. Thermogravimetric technique is used to investigate the erosion-corrosion behavior of uncoated and coated boiler tube steel at high temperature for 1000 hours. SEM/EDAX, XRD and X-ray mapping techniques were used to analyse the corrosion products.
Application
• Gas Turbine and jet Turbine• Nuclear reactors• Power plants• Spacecraft • Chemical processing
Creep
Th = (tcreep+273)/(tmelting +273)Th > 0.5 Creep is a concern
Creep test: measure dimensional changesFocuses on early deformation stages Creep conducts: Const Load Engineering purpose
Stress Rupture test: effects of Temp on long time load bearing characteristics, tr.
• Andrade’s Model• 1.Sudden strain, 2.Transient creepwith
strain rate decrease with time,• 3. const rate creep
• Garofalo Model:
22
• Elevated Temperature Tensile Test (T > 0.4 Tmelt).
• Generally,
time
creep test
xslope = ss = steady-state creep rate.
ssceramics ssmetals sspolymers. . .
MEASURING ELEVATED T RESPONSE
timeelastic
primary secondary
tertiary
T < 0.4 Tm
INCREASING T
0
strain,
• Occurs at elevated temperature, T > 0.4 Tmelt• Deformation changes with time.
23
Adapted fromFigs. 8.26 and 8.27, Callister 6e.
CREEP
0 t
• Most of component life spent here.• Strain rate is constant at a given T, --strain hardening is balanced by recovery
24
stress exponent (material parameter)
strain rateactivation energy for creep(material parameter)
applied stressmaterial const.
• Strain rate increases for larger T,
102040
100200
Steady state creep rate (%/1000hr)10-2 10-1 1s
Stress (MPa)427C
538C
649C
Adapted fromFig. 8.29, Callister 6e.(Fig. 8.29 is from Metals Handbook: Properties and Selection: Stainless Steels, Tool Materials, and Special Purpose Metals, Vol. 3, 9th ed., D. Benjamin (Senior Ed.), American Society for Metals, 1980, p. 131.)
s K2nexp
QcRT
.
SECONDARY CREEP
• Failure: along grain boundaries.
25
time to failure (rupture)
function ofapplied stress
temperature
T(20 logtr ) LL(103K-log hr)
Stre
ss, k
si
100
10
112 20 24 2816
data for S-590 Iron
20appliedstress
g.b. cavities
• Time to rupture, tr
• Estimate rupture time S 590 Iron, T = 800C, = 20 ksi
T(20 logtr ) L1073K
24x103 K-log hr
Ans: tr = 233hr
Adapted fromFig. 8.45, Callister 6e.(Fig. 8.45 is from F.R. Larson and J. Miller, Trans. ASME, 74, 765 (1952).)
From V.J. Colangelo and F.A. Heiser, Analysis of Metallurgical Failures (2nd ed.), Fig. 4.32, p. 87, John Wiley and Sons, Inc., 1987. (Orig. source: Pergamon Press, Inc.)
CREEP FAILURE
• Most of component life spent here.• Strain rate is constant at a given T, --strain hardening is balanced by recovery
24
stress exponent (material parameter)
strain rateactivation energy for creep(material parameter)
applied stressmaterial const.
• Strain rate increases for larger T,
102040
100200
Steady state creep rate (%/1000hr)10-2 10-1 1s
Stress (MPa)427C
538C
649C
Adapted fromFig. 8.29, Callister 6e.(Fig. 8.29 is from Metals Handbook: Properties and Selection: Stainless Steels, Tool Materials, and Special Purpose Metals, Vol. 3, 9th ed., D. Benjamin (Senior Ed.), American Society for Metals, 1980, p. 131.)
s K2nexp
QcRT
.
SECONDARY CREEP
The Creep Test:
• a typical creep curve showing the strain produced as a function of time for a constant stress and temperature.
Apply stress to a material at an elevated temperature
Creep: Plastic deformation at high temperature
The Creep Test:
Master plot for Larson–Miller parameter for S-590 alloy (an Fe-based alloy) (C = 17).
(From R. M. Goldhoff, Mater.Design Eng., 49 (1959) 93.)
Larson-Miller Parameter
Relationship between time to rupture and temperature at three levels of engineering stress, σa, σb, and σc, using Larson–Miller equation (σa > σb > σc).
Larson-Miller Equation
Material Parameters
Flow of vacancies according to (a) Nabarro–Herring and (b) Coble mechanisms, resulting in an increase in the length of the specimen.
Diffusion Creep
• Coble creep: a form of diffusion creep, is a mechanism for deformation of crystalline solids. Coble creep
occurs through the diffusion of atoms in a material along the grain boundaries, which produces a net flow of material and a sliding of the grain boundaries.
Coble creep is named after Robert L. Coble, who first reported his theory of how materials creep over time in 1962 in the Journal of Applied Physics.
The strain rate in a material experiencing Coble creep is given by:
where• σ is the applied stress• d is the average grain boundary diameter• Dgb is the diffusion coefficient in the grain boundary• − QCoble is the activation energy for Coble creep• R is the molar gas constant• T is the temperature in Kelvin
• Note that in Coble creep, the strain rate o is proportional to the applied stress σ; the same relationship is found for Nabarro-Herring creep. However, the two mechanisms differ in their relationship between the strain rate and grain size d. In Coble creep, the strain rate is proportional to d − 3, whereas the strain rate in Nabarro-Herring creep is proportional to d − 2. Researchers commonly use these relationships to determine which mechanism is dominant in a material; by varying the grain size and measuring how the strain rate is affected, they can determine the value of n in o and conclude whether Coble or Nabarro-Herring creep is dominant.
Dislocation climb (a) upwards, under compressive σ22stresses, and (b) downwards, under tensile σ22 stresses.
Dislocation Climb
Dislocation overcoming obstacles by climb, according to Weertman theory. (a) Overcoming Cottrell–Lomer locks. (b) Overcoming an obstacle.
Dislocations Overcoming ObstaclesWeertman Mechanism
(a) Steady-stategrain-boundary sliding withdiffusional accommodations.
(b) Same process as in (a), in anidealized polycrystal; the dashedlines show the flow of vacancies.
(Reprinted with permission fromR. Raj and M. F. Ashby, Met. Trans.,2A (1971) 1113.)
Grain Boundary Sliding
Grain-boundary sliding assisted by diffusion in Ashby–Verrall’s model.
(Reprinted with permission from M. F. Ashby and R. A. Verrall, Acta Met., 21 (1973) 149.)
Ashby-Verrall’s Model
Deformation mechanism maps These are graphs in typically stress-temperature space (but also grain size-temperature and others) which show which deformation mechanisms dominate under which conditions
• Deformation mechanism maps • These are graphs in typically stress-
temperature space (but also grain size-temperature and others) which show which deformation mechanisms dominate under which conditions
Superplastic tensile deformation in Pb–62% Sn eutectic alloy tested at 415 K and a strain rate of 1.33 × 10−4 s−1; total strain of 48.5.
(From M. M. I. Ahmed and T. G. Langdon, Met. Trans. A, 8 (1977) 1832.)
Superplasticity
(a) Schematic representation of plastic deformation in tension with formation and inhibition of necking. (b) Engineering-stress– engineering-strain curves.
Plastic Deformation
Strain-rate dependence of (a) stress and (b) strain-rate sensitivity for Mg–Al eutectic alloy tested at 350 ◦C (grain size 10 μm).
(After D. Lee, Acta. Met., 17 (1969) 1057.)
Strain Rate Dependence
Tensile fracture strain and stress as a function of strainrate for Zr–22% Al alloy with 2.5-μm grain size.
(After F. A. Mohamed, M. M. I. Ahmed, and T. G. Langdon, Met. Trans. A, 8 (1977) 933.)
Fracture
Effect of strain-rate sensitivity m on maximum tensileelongation for different alloys (Fe, Mg, Pu, Pb–Sr, Ti, Zn, Zr based).
(From D. M. R. Taplin, G. L. Dunlop, and T. G. Langdon, Ann. Rev. Mater. Sci., 9 (1979) 151.)
Effect of Strain Rate Sensitivity
Cavitation in superplasticity formed 7475-T6 aluminum alloy (ε = 3.5) at 475 ◦C and 5 × 10−4 s−1. (a) Atmospheric pressure. (b) Hydrostatic pressure P = 4 MPa. (Courtesy of A. K. Mukherjee.)
Cavitation in Superplasticity
(a) Effect of grain size on elongation: (A) Initial configuration. (B) Largegrains. (C) Fine grains (10 μm) (Reprinted with permission from N. E. Paton, C. H.Hamilton, J. Wert, and M. Mahoney, J. Metal, 34 (1981) No. 8, 21.)
(b) Failure strainsincrease with superimposed hydrostatic pressure (from 0 to 5.6 MPa). (Courtesy ofA. K. Mukherjee.)
Effect of Grain Size on Elongation
Microstructure of a Creep resistant steel
Heat Resisting SteelPrecipitates
M23C6 , M7 C3 , M2X ,
M3 C , M6 C , M X
IntermetallicsLaves Phase, Z-Phase
Alloying ElementsSubstitutional :
Cr, V, Nb, Mo,W, Cu, Mn
Interstitial : C, N
Creep Resistant Steel
MicrostructureTempered Martensite, Bainite
Resistance to Creep
Þ Solid solution hardeningÞ Precipitate hardeningÞ Microstructure
• Thanks