advanced high temperature alloys

5/24/2018 Advanced High Temperature Alloys

1/123University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and Alloys1

Prof. Dr.-Ing. Uwe GlatzelMetals and Alloys

University BayreuthSS 2014

Advanced High

Temperature Alloys



Lecturer:

Prof. Dr.-Ing. habil. Uwe Glatzel born Dez. 1960

Physik-Diplom (B.Sc. and M.Sc) in Tbingen

(exchange year in Corvallis, Oregon, USA)

PhD thesis at the Institute for Metals Research, TechnicalUniversity Berlin, Prof. Monika Feller-Kniepmeier

post-doc (1 Jahr) at Stanford University

Habilitation TU-Berlin

Gerhard-Hess award of the German Science Foundation

(DFG) for young scientist (400.000 )

1996-2003 full professor for Metals and Alloys, Jena

since April 2003 Bayreuth (Chair for Metals and Alloys)postal address:

Ludwig-Thoma-Str. 36b phone: +49 (0) 921 - 55-5555

D-95447 Bayreuth, Germany e-mail: [email protected]



R. Brgel,Handbuch Hochtemperatur-Werkstofftechnik, Vieweg R.C. Reed, The Superalloys - Fundamentals and Applications, Cambridge Univ. Press

M.J. Donachie, S.J. Donachie, Superalloys - A Technical Guide, ASM International

H. Frost, M.F. Ashby,Deformation-Mechanism Maps, Pergamon Press

M.F. Ashby,Materials Selection in Mechanical Design, Elsevier

G. Meetham, M. Van der Voorde,Materials for High Temperature Engineering Applications, Springer

J. Betten, Creep Mechanics, Springer

R.E. Reed-Hill,Physical Metallurgy Principles, PWS-KENT Publishing

D.R. Askeland: Materialwissenschaften, Spektrum Lehrbuch; 1994

W.D. Callister: Materials Science and Engineering - An Introduction, Wiley, New York, 1999

H. Schumann,Metallographie, Deutscher Verlag fr Grundstoffindustrie, Leipzig

F. Vollertsen, S. Vogler, Werkstoffeigenschaften und Mikrostruktur, Hauser Verlag

P. Haasen,Physikalische Metallkunde, Springer-Verlag, Berlin

H.-J. Bargel, G. Schulze, Werkstoffkunde, VDI-Verlag, Dsseldorf

P. Sarrazin, A. Galerie, J. Fouletier, Mechanisms of High Temperature Corrosion, Trans. Tech. Publ.

N. Cumpsty,Jet Propulsion, Cambridge Univ. Press

Literature

lecture notes: http://www.metalle.uni-bayreuth.dethen "Lehre" then "Vorlesungen",

you will find the link to this lecture notes and three review talks we will do at the end.



What You Should Know:

basic thermodynamics

introduction to diffusion

introduction to dislocations phase diagrams

theory of elasticity

... basic materials science courses



1. Introduction, Basics

2. Stability of Microstructure

3. Mechanical Properties

a) Staticb) Cyclic (Fatigue)

4. High Temperature Corrosion

5. High Temperature Alloys6. Lost Wax Investment Casting

7. Depending on Time: Lectures on

a) SX Ni-Base Superalloys b) LEK 94 c) Pt-Base Superalloys

Content



Introduction

only alloys will be looked at (no ceramics, no

polymers).

no coatings (BUT : practically all high

temperature systems are coated!), simply not

enough time.



Motivation for High

Temperature Alloys

efficiency of Carnot heat enging

(with hot and cold temperatures). Several research

projects related to jet engines, stationary gas turbines

and waste-to-energy plant are carried out within my

group with the goal to increase Th.

melting processes (glass, metal, ... ).

chemical process (PTFE, ... ).

many other applications ...

jet engines, see Single Crystal Ni-Base Superalloys

max

minmax

TTT =



Maximum Temperatures for

Applications of Different Materials

Groupmaximum service temperature

[C]deformation/damage mechanism

Polymer up to 300 melting, decomposing (pyrolyze)

Glass up to 800 viscous flow

Metals

Fe-Basis (coated) up to 1100Fe-ODS up to 1300

Ni- and Co-base up to 1200

Pt-base up to 1600

refractory metals in inert

atmosphere above 1600

MoSi2up to 1800

creep, dislocation climb,

grain boundary sliding

Ceramics SiC up to 1600

viscous flow, glass transition

temperature, grain boundary

sliding

Composits (SiC/C) up to 1600 complex



Overview Materials

temperature [C]500 1500 2000

usable

strength

source:

Plansee AG,

Reutte,

Tirol,

Austria



Taking Density into Account

500 1500 2000temperature [C]

usable

strength



Oxidation Resistance

500 1500 2000temperature [C]

usable

stren

gth


12/123University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and Alloys

Tmof platinum

Refractory Metals:

12

Most common definition ofrefractory metals (refractory =

widerspenstig, halsstarrig):

two elements of the 5. and

three elements of the 6. period

with melting points higher

than Pt. Processing in general

by powder metallurgy.

wider

definitionof

refractory

metals



Density

13

Ru, Rh, Pd

Re

W

Ta

Hf

Pt

Au

Tc

Mo

Nb

Pd

Ag

Os, Ir

Ni



Abundance of Elements

14

to find 1 Rh atom

within a bunch of

Si-atoms is

comparable to

find one

individual person

within the word

population U.S. Geological Survey Fact Sheet 087-02 (2002)



Material Choice

temperature

environment

moving/non-moving part

design complexity (how to manufacture)

price constrictions (depending on application

of system). Reduction of 1 kg in weight:car ~ 0 - 5

plane ~ 100 500

aerospace ~ 100.000 - 500.000



Influence of ... on ...

temperature: phase transitions, volume fractions, ...

diffusion (recrystallization, dislocation climb, diffusional creep, ... )

thermal fatigue (TF)

mechanical: creep

fatigue (low cycle, LCF, high cycle fatigue, HCF)

environment:

oxidation corrosion

combinations:

thermo-mechanical fatigue (TMF)

stress corrosion cracking, stress oxidation, ...


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University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and Alloys17

Basics

Thermodynamics KineticsBoltzmann-statistics: energy of

movement increases with temperatureTk

2

3u Batomkin =

TR

Q

0 e

=

Tk3Tk2

32u2u BBatomkinatomtotal ===

Arrhenius-plotTR3Umol

total = 0,33 eV, bzw. 32 kJ/mol bei 1000C


18/123


Vacancy Concentration

F = U - TS non-zero vacancy concentration is

in thermodynamic equilibrium

T[C] 20 300 450 800 1000 1200 1454

T/Tm 0.17 0.33 0.42 0.62 0.74 0.85 1.00

cv 10-23 310-12 10-9 10-6 10-5 710-5 310-4

TR

Q

v

vac

ec

= Qvacnickel= 1,36 eV (energy necessary to create one vacancy)

equilibrium vacancy concentration for nickel


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Nickel Vacancy Concentration


temperature [C]

0 200 400 600 800 1000 1200 1400 1600

vacancyconcentration

100

10-5

10-10

10-15

10-20

10-25

Tm


temperature [C]

0 200 400 600 800 1000 1200 1400 1600

vacancyconcentration

[10-4]

1,00

0,75

0,50

0,25

0,10

Tm

Tk

Q

vB

vac

ec

=

with:

Qvacnickel= 1,36 eV

kB= 8.60210-5eV/K

Tm/2


20/123


Diffusion

cDj =

1. Fick's law

[j] = (atoms) m-2 s-1

[D] = m2 s-1

[c] = (atoms) m-3

vacancy diffusion or

volume diffusion


21/123


Coefficient of Diffusion

Qvac energy to create a vacancy

Qmigration activation energy to migrate a vacancy

Qsd activation energy for volume diffusionQsd= Qvac+ Qmigration

Tk

Q

Tk

QQsdmigrationvac

eDeDD

+

== 0

)(

0

Qsd 17 kB Tm Qsdnickel 2.5 eV = 244 kJ/mol

(for a perfect crystal; defects will lower the activation energies)


22/123


Qsdversus Tm

400 kJ/mol

0.137 kJ/(molK)

17 kBNA


23/123


Dependence Melting Point and

Enthalpy of Vacancy Creation

elementTm

[C]17RTm

Qvac

[eV]

crystal

structure

Pb 327 0.88 0.57 fcc

Al 660 1.36 0.68 fccCu 1 085 1.99 1.29 fcc

Ag 1 235 2.21 1.12 fcc

Ni 1 455 2.53 1.78 fcc

Pt 1 768 2.98 1.32 fcc

Mo 2 623 4.23 3.00 bcc

W 3 422 5.40 4.00 bcc


24/123


Coefficient of Diffusion

Steep slope indicates a

high activation energy.

Small elements diffuse

faster.

Diffusion in fcc crystals

slower than in bcc crystals.

fcc

-iron bcc

-iron


25/123


Coefficient of Diffusion with Defects

Coefficient of diffusion of Th

in W.

Overall velocity for diffusiondepending on grain boundary

thickness, grain size and

dislocation density.

surface diffusion

grain boundary diffusion

volume diffusion

pipe

diffusion


26/123


Pipe Diffusion

Deff= Dsd+ adisl. Ddisl.

adisl. area of dislocation core

( 5b2 0.3 nm2)

dislocation density

Ddisl. pipe diffusion along

dislocation core

atom flux ~ Darea

dashed line: diffusion in crystal by the velocity of pipe diffusion

2~ grainsd

grain

dDtimeatoms

nbDdD2

.disl

2

grainsd =identical atom fluxes if:

nbD~time

atoms 2.disl

.disl

volume diffusion

dominant

pipe diffusiondominant

increasing

decreasing

disl.

disl.

sd

grain

2

.disl

sd

d

b

D

D =


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Grain Boundary Diffusion

Deff= Dsd+ / d Dgrain bound.

with:

effective grain boundary

thickness ( 2 b 0.5 nm)

d grain size

Ddisl. pipe diffusion along dislocation

core

dashed line: diffusion in crystal by the velocity of grain boundary diffusion

volume diffusion

dominant

grain boundary diffusion

dominantfine

grain

coarse

grain

gb

sd

gb

graingb

2

grainsd dDdD =identical atom fluxes if:graingb

sd

dD

D =


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Diffusional Creep

Nabarro-Hering creep (pure volume diffusion)

Coble creep (grain boundary diff.)

Tkd

D2

2

grain

diffusionself

NH

=

Tkd

D

2 3grain

boundarygrain

C

=

thickness of grain boundary, atomic volume

NH-c

C-c


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Combined NH and Coble Creep:

2

grain

eff

3

grain

boundarygrain

2

grain

diffusionself

CNHcreepdiffusiond

D

Tk~

d

D

d

D

Tk2

+

=+=

for real geometry (non-cuboidal grains)

grain

boundarygrain

diffusionselfeffd

DDD

+=

grain

gb

sdd

DD

=identical creep rates if:

graingb

sd

dD

D =


30/123


Activation Energies Indicating

Mechanism Changes

Single crystal aluminium, oriented such that {111} slip is activated.

Lytton, Shepard and Dorn, Trans. AIME212(1958) 220

~ Qsd


31/123


Diffusion in Ordered Structures

(Intermetallic Phases)

High binding energieshigh activation energieslow coefficient of diffusion

Example NiAl: very high enthalpy of ordered B2

structurehigh enthalpy outweighs low entropyordered up to Tm

TmNi= 1,455CTm

Al= 660C

TmNiAl= 1,638C


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Second Fick's Law

cDt

c=

Can be concluded directly from first Fick's law.

Similar in heat transfer systems, electrical

potential, ... .

0. 5 1 1. 5 2

0. 2

0. 4

0. 6

0. 8

1

f1(x)

f2(x)

f3(x)

( )x1)x(f1 =

=

5.0

x1)x(f2

=05.0

x1)x(f3

( )

=

tD2

xccc)t,x(c 011

solution to these

boundary conditions:


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Thermal Conductivity

The most simple, stationary case: no heat radiation, constanttemperatures in front and back of component.

coefficient of heat (or thermal)

conductivity: = a cp

a coefficient of temperature conductivity

cp heat capacity

density

... coefficient of heat transfer

cDj =

Tq =

cDt

c=

Tat

T=

compare:


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Temperature Distribution with

Thermal Barrrier Coating (TBC)

Wrmedmm-

schicht

Haftvermittlerschicht Grundwerkstoff

hot air

cooling air

TBC bond coat substrate

In case of transients, the temperature should reach a stable distribution as fast as possible in

order to reduce thermal stresses (temperature conductrivity as high as possible).

In case of stationary circumstances, heat conductivity leads to heat flow into the solid.


35/123


Material Parameters at RT

Km

W

KkgJ

3

cm

g

s

m10

26

material/property

heat cond.

heat cap.cp

density

temp. cond.a

ferritic steel 45 460 7.8 13.0

austenite steel 15 500 8.0 3.8

Ni-base alloys 11 450 8.2 3.0

Mo 145 240 10.2 59.0

Ti alloys (-rich) 7 530 4.5 2.9

Al 210 890 2.7 87.0

Al2O3bei RT

( Al2O3bei 1000C )

25

( 6)

800 3.9 8.4

source: Brgel

Attention: Heat conductivity strongly depends on alloy composition, see steels and pure

Ni with 91 W/(mK)in comparison to Ni-base alloys with 11 W/(mK)


36/123


Content

1. Introduction, Basics2. Stability of Microstructure








37/123


Microstructure is NOT stable

annealed deformed

stress-relieved recrystallized


38/123


Recrystallization

time dependence of

recrystallization can be

approximated by

Avrami-Johnson-Mehl

function:

n

0tt

r e1f

=

, deformed

partly re-crystallized

fully re-crystallized


39/123


Grain Coarsening

driving force: reduction of grain boundary

energy

T > 0.7 Tm

no pre-deformation necessary

self-similar system

Ostwald ripening d ~ t1/3

(big grains eat upsmall grains)

new grains have low dislocation density


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Grain Coarsening

monomodal

bimodal (some grain

boundaries are pinned,

e.g. by precipitates)


41/123


Precipitate Hardening

Requirements:

solid solution at higher

temperatures (ability to

homogenization heat

treatment)

during cooling a two-phase

region should be reached

in general: cooling rate as

high as possible, thereafterannealing (in the two-phase

region) to let grow the

precipitates

solution heat treatment

quenching

annealing

furnace cooling


42/123


Thermodynamic Kinetic


43/123


Example: Al-Cu Alloy

Guinier-Preston

Zones leading to

-Precipitates

(Al2Cu) have

paved the way

to the success ofAl-alloys

solution heat treatment

quenching

annealing

quenching

annealing

supersaturated solid solution

Other Examples of


44/123


Other Examples of

precipitate hardening:

nickel-base superalloy

Al2Cu in AlCu alloy:

platinum-base superalloy

Ti D d f


45/123


Time Dependence of

Precipitation Hardening

dT precipitate size T distance between precipitates

fT volume fraction of precipitates

nucleation, growth, coarsening

T = const.


46/123


Coherent - Semicoherent - Incoherent

misfit( ) a

a

a

aa

a

aa

aa

aa:

p

mp

m

mp

mp21

mp

+

=

(mit Orientierungsbezug) (ohne Orientierungsbezug)

E C id ti f


47/123


Energy Consideration for


Gtotal= Gvol+ Gboundary+ Gstrain+ Gdefect

total change in free enthalpy

enthalpy of formation of matrix to precipitate (scales with volume)

enthalpy of phase boundary (scales with surface)

strain enthalpy (elastic energy + dislocation line energy)

reduction of enthalpy by precipitation coupled with a defect


48/123


Heterogeneous Nucleation

dislocationssubgrain

boundaries

stacking faults

coherent

twin boundaries

incoherent

vacancy cluster

surface (internal

and external)

grain boundaries

precipitates


49/123


TEM-Micrograph of TiC Precipitates at

Dislocations in an Austenitic Steel


50/123


Ostwald-Ripening of Precipitates

d3- d03~ Dt here for T/Tm0.74

' particle size in IN 738 LC at

T = 920C.

particle coarsening constant of50 nm h-1/3

+0,5 m after 1.000 h

+1 m after 8.000 h

1 year


51/123


Content








( )


52/123


Room Temperature (RT) versus

High Temperature (HT) Deformation

most alloy properties at room temperature are time and

rate independent (elastic constants, tension stress, ... ),

tension stress experiment.

For T > 0.4 Tmthe properties (deformation) will be timetemperature and rate dependent, creep experiment.

deformation hardening fine grain hardeningsolid solution

strengthening

precipitate

hardening

cold deformation (RT) strong medium medium to strong medium to strong

creep (HT)

temporary hardening,

reduced creep rupture

strength, may lead to

recrystallization

reduced strength with

fine grain material

coarse grain,

better single crystal

medium medium to strong

El ti (E )M d l d


53/123


Elastic (E-)Modulus and

Poisson's Ratio

)1(2

EG

+=shear modulus G

Ni-base superalloys 120 115 110 105 0,39 - 0,41

85 @ 1000C

Change in Materials Properties


54/123


Change in Materials Properties

with Temperature

Material properties of steel and

Ni-alloys at elevated

temperatures. Comparison

between short-term and long-

term parameters.


55/123


Tension Creep Experiment

(UTS)

(YS)

design by YS or UTS

design by t1%


56/123


High Temperature Deformation

dislocation glide (Peierls stress, in fcc and hcp very small and for T >

0.15 Tmnegligible)

cross slip of screw dislocations and dislocation interactions (for a low

stacking fault energylarger dislocation spacingthermal

activation necessary, T > 0.2 Tm, influence on deformation rate)

climb of edge dislocations to overcome obstacles:

diffusion at complete

dislocation line

T > 0.4 Tm


57/123


Dislocation Climb

climb of edge dislocations to

annihilate each other.

arrangement in low energyconfigurations (sub-grain

boundaries), climbing around

abstacles (leaving the glide

plane)

movement of screw

dislocations with kink
http://c/Users/Uwe%20Glatzel/Documents/W/Vorlesungen/SS09/Advanced%20High%20Temperature%20Alloys/4-Douglas.wmv


58/123



59/123


Internal Back Stress

Dislocations climb allows annihilation of dislocationsand to establish a constant dislocation density,

resulting in an internal back stress of:

dislocation= and

G shear modulus, constant 0.3 - 1, b magnitude of Burgers vector

= bG.int

r

1

2

bG

r

1=


60/123


Creep Experiment

behavior of pure metals:

primary secondary tertiary:

Creep Experimental Setup


61/123


Creep Experimental Setup

up to 1400C

Constanttemperature

and stress or

load

Creep Experimental Setup for
http://c/Users/Uwe%20Glatzel/Documents/W/Vorlesungen/1200%C3%AEmpg


62/123


Electrical Conductivity Material

up to Melting Temperature

Pyrometer from left, optical strain

measurement from right, both contact-free.


63/123


Interrupted creep tests

[001] orientation, 1123K, 650MPa

time [h]

0 10 20 30 40 50 60 70

strain[%]

0

1

2

3

4

5

6

7

single crystal (SX) nickel base superalloy (habilitation thesis Glatzel)

[001] orientation, 1123K, 650MPa

time [h]

0 10 20 30 40 50 60 70

strain

rate

[1/s]

0

2x10-6

4x10-6

6x10-6

8x10-6

1123K, 650 MPa

strain [%]0 1 2 3 4 5 6

strainr

ate

[1/s]

10-7

10-6

10-5

logarithm of strain rate versus strain

(most valuable information for

materials scientist)


64/123


Different Creep Stages

primary creep: strain rate d/dt decreases

material hardens

secondary creep stage: strain rate constant

hardening and softening are in equilibriumdislocation multiplication and annihilation in

equilibriumdisl. density = const.

tertiary creep: necking (creep pores) developlocal stress and strain rate increases

drastically.

World Record


65/123

University Bayreuth, Advanced High Temperature Alloys Uwe Glatzel, Metals and Alloys

World Record

Japan, Germany

65

http://www.nims.go.jp/eng/news/press/2011/02/p201102240.html

NIMS: 14.853 days on 24. Feb. 2012,

probably still running (started in 06/1969!)

Siemens: 14,852 days terminated in 2000

Modelling of Primary and


66/123


Modelling of Primary and

Secondary Creep Stage

66

density velocity

vb =


67/123


Problem with Low Creep Rates

Life time of stationary gas turbines > 20 years andmax.= 3%

510-11s-1

Reliable data in lab down to 110-9s-1:

l= 1 mwith l0= 25 mm after 10 h

3.5% strain per year!

Within university labs we are two orders of magnitude too

fast compared to real life of a stationary gas turbine!

statesteady


68/123


Engineering Creep Curves

raw data creep curves:

time to failure:

isochrone time to failure:

time strain

(e.g. 1%)

isochrone strain

l C


69/123


Natural Creep Law

vbstatesteady =

2

external

bG

1

external~v

natural creep lawbG

~2

3

external


70/123


Norton Creep Law (Empirical)

TR

Q

n

externalstatesteady

creep

eA

=with Norton creep exponent "n"

and Qcreep Qself diffusion

power law break

down (plb)

T = const.

dislocation

climb

diffusional creep

stress dependence

of the stationary

creep rate of the

austenitic steel 800

H at 900C and

1000C:

Temperature Dependence of


71/123


Temperature Dependence of

Stationary Creep Rate

= 28 MPA = const.

fcc alloys:

TR

Qcn

5,3

SFs eE

A

=

Austenitischer Stahl 800H

QsdNi 244 kJ/mol

QsdFe 290 kJ/mol

i i f


72/123


Activation Energy for Creep

slope = 1


73/123


Constant Load Constant Stress

failure

in case the gauge length

deforms uniform withconstant volume

( )nn00

n

0

0

n

0n

0 1A

)1(FAF +=

+=

==

ln = ln + n ln 0+ n ln (1+) = const. + n ln (1+) 0

This method is applicable to

determine the stress exponent "n"

only, if the secondary creep state

lasts to at least 10%

Ashby Deformation


74/123


Ashby Deformation

Mechanism Maps

n = 3

Ashby Deformation


75/123


Ashby Deformation

Mechanism Maps

Versetzungsklettern !dislocation climb !

D f ti M h i


76/123


Deformation Mechanisms:

Elastic Deformation: Spontaneous and reversible deformation. In the elastic region: = E(rule of

thumb: e, max10-3, but definitely 0.4Tm) and lower stress levels dislocation climb plays the

major role => time dependent constant strain rate (d/dt)ss~ n, with a Norton stress exponent in-between

3 und 8.

Diffusional Creep: In principle over the complete temperature regime (0 K - Tm). Relevance only at very

low stress levels and T close to Tm: Coble-creep (grain boundary diffusion). For geological times a time

dependent deformation can be determined. Transition to Nabarro-Herring creep (volume diffusion) is

dependent on grain size and grain boundary thickness. The transition temperature from coble to Nabarro-

Herring creep can be explained by the different activation energies of volume and grain boundary diffusion.

Creep of Alloys


77/123


Creep of Alloys(assuming solid solution, no precipitates)

a) interaction dislocation

and impurity (low temp.)

b) stationary dislocation

pinned by impurities

(Cottrell clouds)

c) pulled off Cortrell clouds

(Lders bands)

d) gliding dislocation trails

impurities behind (viscous glide)

e) impurities faster than dislocation (very high temp., no hardening)

f) annihilation due to dislocation climb

solutionsolidi bG +=

P i it t H d i


78/123



eprecipitatsolutionsolidi bG ++=

threshold stress concept (with n 3 - 4 and Qcreep= Qself diffusion):

TR

Qcn

0ss e

EA

=

mechanism temperature

coherent and semi-

coherent phase

boundaries

in-coherent phase

boundaries

cutting 0 K up to Ts yes no

bypass by Orowan 0 K up to Ts yes yes

climb over obstacles > 0.4Ts yes no

O St


79/123


Orowan Stress

79

L

bG

Orowan

r

2r

TT

L

Tsin

Line tension leads to a back stress,

the Orowan stress, due to obstacles

(in most cases precipitates) with an

average distance L between these

precipitates.

Hardening Mechanisms as


80/123


g

Function of Precipitate Size

dT0 initial precipitate size

1and 2arbitrary external stress levels

passing by:

climbing:

Cutting is relevant only for coherent

precipitates

Dependence of stationary creep rate on

initial precipitate size for two different

external stress levels

Td~

2

Td1~

= cutting

Pinning of Dislocations by


81/123


g y

Carbides in Austenitic Steel

T = 1000C, = 25 MPa, carbides of the type TiC und M23C6

V Hi h V l F ti


82/123


Very High Volume Fractions

Volume fractions of 70% are only achievable with non-spherical precipitates.Spacing between precipitates is getting smaller Orowan stress

Orowan Gb/L necessary. For small strains precipitates are not cut by

dislocations. With G = 90 GPa, b = 0.25 nm, L 75 nm => Orowan 300 MPa

nickel base superalloys

ODS alloys:

Orowanpart.

3'

d

fbG

Dispersion Hardening


83/123


Dispersion Hardening(oxide dispersion strengthened alloys (ODS-alloys))

back-side pinning of dislocation by

ODS-particle (Rssler + Arzt)

precipitate strengthened

dispersion strengthened

yield

stress

temperature Tm

temperature regime for

dissolution of precipitates

Summary:


84/123


Hardening Mechanisms

84

Internal back stress in steady state regime:

Orowan stress in case of precipitates or particles: Orowan Gb/L

Solid solution strengthening:

In case of coherent precipitates:

= bGi

r

rconst. solutionsolid

EEa

a misfitcoherency =

Creep Damage


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Creep Damage

a) cracks at grain boundaries b) cavities (micropores) at grain boundaries

creation of a creep pore in poly-crystalline material due to disloction glide:

Creep Damage


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Creep Damage

nucleation, not detectable with OM

micropore, difficult to detect

pear necklace like chain of

micropores (easy detectable)

micro cracks

fracture

Extrapolation of Time-to-Fracture Data


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p

(Larson-Miller plot, Larson-Miller parameter)

m

ss

f

Kt

=

Monkmann-Grant relation with constant K and exponent m 1:

( )ssf lnmK)tln( =

TR

Q

TR

Q

n

0ss

creepcreep

eBeA == T1BB)ln( 21ss =

TPC

TmmKtf

11)ln( 21 +=+= BB

with material dependent constants C and P.

Larsson-Miller plot: P = T[C + ln(tf)]10-3, with CNi-base= 20, T in K, tfin h

Example: tf=100 h, T = 1273 K P = 31.3 (relation tfwith T at = const.)

~ 1952 @ GE

Larson Miller Plot


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Larson-Miller-Plot

P = T[20 + ln(tf)]10-3(T in K, tfin h)

Comparison of CMSX-6,

LEK 94 and CMSX-4,

patent Wllmer, Glatzel,

Mack, Wortmann

stationary gas turbine, about 20 years of service ~ 130.000 h

Comparison LEK 94 with


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CMSX-4 and CMSX-6

Larsen-Miller-parameter

P = T (20+log tf) 10

-3

25 26 27 28 29 30 31 32

stress[M

Pa]

120

230

500CMSX-6 [Wortmann 88] 8.0 g/cm3

CMSX-4 [Erickson 94] 8.7 g/cm3

CMSX-4 [Frasier 90] 8.7 g/cm3

LEK-2 8.5 g/cm3

LEK-4 8.2 g/cm3

LEK-5 8.2 g/cm3

LEK-3 8.1 g/cm3

LEK-6 8.3 g/cm3

LEK-1C 8.4 g/cm3

LEK-1B 8.3 g/cm3

LEK-1A 8.2 g/cm3

T = 10 K

24K

10 K

29K

Not correctedregarding density!

Content


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Content





5. High Temperature Alloys

6. Lost Wax Investment Casting



Time Dependent Variation of Stress


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and/or Temperature and/or ...

Whler diagram for T < 0.4Tm. Z time fatigue limit, D endurance

fatigue limit

a) type I metal (bcc) b) type II metal (fcc) endurance limit at 2107

Change in Whler Diagram with


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Temperature and Holding Time

10 CrMo9-10

Thermal Fatigue


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Thermal Fatigue

Thermal breathing of turbine blade:

a) heating phase: edges reach high temperatures faster than interior

b) cooling phase: edges cool faster than interior

c) repeated thermal cycles lead to thermal fatigue cracks at edges

Thermal Strains and Stresses :


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Thermal Strains and Stresses :

thermal= thermal T, or: thermal= E thermal

thermal= E thermal T

Lower E-Modulus is Helpful:


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Lower E-Modulus is Helpful:

orientation of single crystals in direction reduces thermal stresses

Anisotropy and Temperature Dependence of


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Elastic Constants in Ni-base Superalloys

96

Orientation dependence of

Youngs modulusE of matrix

phase. Distance from the center to

the surface indicates the

magnitude of the Youngs modulus

in this direction.

D. Siebrger, H. Knake, U. Glatzel, Mat. Sci. Eng. A298 (2001)

TMF and many other Time


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Dependent Test Techniques

Can not be covered in this lecture!

Content


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Content









High Temperature Corrosion


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High Temperature Corrosion

oxidation: external and internal, passivation

carburization (internal carbides)

nitration: internal, seldom nitrite passivation

sulfurization: external (sometimes

passivation), seldom internal

Worldwide 1 ton iron per minute corrodes to rust (low

temperature aqueous corrosion).

Ellingham-Richardson-Diagram


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Ellingham Richardson Diagram

right hand and lower axes

O2partial pressure at T = 0.

As an example pO2of10-15Pa = 10-20bar = 10-17mbar

is shown as a dashed line.

only the oxides below this line

are thermodynamic stable.

UHV

HV

air

Time Dependent Oxidation


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Time Dependent Oxidation

Oxidation Mechanisms


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Oxidation Mechanisms

logarithmic (not shown)low temperature oxidation whicheventually comes to a stop or no measurable increase in oxide scale

thickness (e.g. Al, Cr, Mg).

parabolic mass change (m/A)

2

~ t. Diffusion through oxidation layereither oxygen or metal. Most favorable oxidation behavior (Al

passivation at high temperatures).

linear mass change: oxide layer with crackscontinuous contact

with metal (e.g. Ta, Nb).

mass loss: volatile oxidescatastrophic oxidation (e.g. V, Mo, W,

Cr, Pt). You can see it inside a broken light bulb.

Pilling-Bedworth Ratio


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Pilling Bedworth Ratio

PB = (volume of oxide of one metal atom)/(volume of metal atom)

ideal is 1.1 to 1.3

Of course thermal expansion coefficients also play a major role for the stability of oxide scales.

Oxide TiO MgO Al2O3 MgO2 Ti2O3 ZrO2 Ti3O5 NiO FeO TiO2 CoO

PB 0.70 0.81 1.28 1.34 1.50 1.56 1.65 1.65 1.70 1.73 1.86

Oxide Cr2O

3 FeCr

2O

4 Fe

3O

4 Fe

2O

3 SiO

2 Ta

2O

5 Nb

2O

5 W

PB 2.05 2.10 2.11 2.15 2.15 2.50 2.68 3.40

Alloying Effects:


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Alloying Effects:

different elements have

different oxygen affinity

concentration changes

diffusion rates are different

oxide layer contains othermetals

Example Ni-Cr-Al


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Example Ni Cr Al

Ni Cr 10 Al 5oxide layer and

internal

oxidation occurs

1000C

Observations for the

S ll R N5


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Superalloy Rene N5

Bensch et al., Acta Mat. 2010

and Acta Mat. 2012

layer number layer composition properties

1 cover oxide layer NiO, CoO thick and porous monophase layer

2 interlayer of oxides NiAl2O4, NiTa2O6, Cr2O3 thick and porous layer consisting of two fractions

3 third oxide layer Al2O3 dense and thin monophase layer

4 -free layer see Tab. 1 Al-content of 2.2 wt. %

5 reduced layer composition in-between layer number 4 and 6 reduced Al content, morphology change

6 two-phase centre region nominal composition of Ren N5 (Tab. 1) regular / structure, seeFig. 6 f)

Content


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Content



a) Static

b) Cyclic (Fatigue)






High Temperature Alloys


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High Temperature Alloys

T > 500C, Application in:

energy generation

engines (cars, trains, airplanes, ships, ... )

chemical industry

metallurgy

mechanical engineering

Overview Metals


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Overview Metals

ele

m.

struc-

ture

Ttrans.

Tm

[C]

[g/cm3]

max. O-solubility

[at.%]

advantages/disadvantages

Ti hdp

krz

882

1855

4.5

4.5

31.9

8

+ low density

+ high melting point

+ abundant available

+ low th.(~ 10-5K-1)

no alloy known with adequate strength for temperatures > 600C

high oxygen and nitrogen solubility > 700C, increased brittleness

linear oxidation > 800C

low thermal conductivity

ignition hazard

V krz 1910 6.1 17 catastrophic oxidation; Tm(V2O5) = 658C

Cr krz 1863 7.2 0.0053 very brittle at RT; conventionally not processable

Mo krz 2623 10.2 0.03 + very high creep strength

+ lowth, high thermal conductivity, good thermal fatigue strength

very brittle at RT

catastrophic oxidation; Tm(MoO5) = 795Cno long lasting coating available

W krz 3422 19.3 0 + highest melting point of metals (only C with even higher Tm)

+ very high creep strength

+ low th, high thermal conductivity, good thermal fatigue strength

very brittle at RT

catastrophic oxidation > 1000C durch hohe WO3-Abdampfrate

no long lasting coating available

very high density

Overview Metals


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Overview Metals

elem. structure Ttrans.Tm

[C]

[g/cm3]

max. O-solubility

[at.%]


Fe

krz

kfz

krz

912

1395

1538

7.9

7.7

7.4

0.0008

0.0098

0.029

+ very good corrosion resistance by alloying with Cr or (Cr + Al)

+ -structure can be stabilized down to RT (by Ni)

+ very good processable and weldable

+ low cost (~ 1 /kg)

strength at high temperatures (> 700C) limited

Co hdp

kfz

422

1495

8.8

8.7

0

0.048


+ Co-alloys castable in air good weldability

only moderate hardening available

Ni-additions necessary to stabilize fcc structure, reduces strength

Ni kfz 1455 8.9 0.05 + broad possibilities for alloying, high strength increase possible by

alloying with Al, leading to '-phase (Ni3Al)


+ processable

relatively low melting pointth.high, low thermal conductivity

Pt kfz 1772 21.5 0 + high corrosion and oxidation resistance


very high density

very expensive (~ 33 /g)

Evolution of materials

d i i


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used in aero-engines

111

The earlier approach of technology transfer from military to civil istending to switch direction.

www.azom.com

Example of Intermetallic

Ph (Ni Al S t )


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Phases (Ni-Al-System)

Ni-Al Intermetallic Phases


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phase structure Ttrans.

Tm[C]

[g/cm3]


Ni3Al L12 1383 7.5 + anomalous temperature dependence of strength

+ same structure base than Ni matrix (fcc)

+ stable for larger Al variations > 1 wt.% Al

+ ductile as single crystal

high density

brittle as polycrystal (can be hindered by boron doping (grainboundary strengthener)

Al-content not sufficient to build stable Al2O3-layerreduced high

temperature oxidation resistance

NiAl B2 1638 5.85 + very good oxidation resistance, since 30 wt.% Al


+ low density

+ ordered structure up to melting point+ high thermal conductivity

+ low coefficient of thermal expansion

extremely brittle at temperatures below 500C (von Mises criterion

not fulfilled)

low strength at high temperatures

NiAl, B2 Ordered

I t t lli Ph


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Intermetallic Phase

At a first sight very interesting (seeadvantages) but despite many efforts and many

100 Mio. US$ research money spent, up today

no bulk usage of NiAl has been achieved.

BUT: aluminum coatings leading to NiAl

layers is heavily used.

Content


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Content



a) Static

b) Cyclic (Fatigue)






MTS-Factory in Bayreuth


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y y

ground-breaking ceremony: 20.02.2008, topping-out ceremony: 06.06.2008

start of production: ~ 12/2008

MTS-Factory, June 2008


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y,



118/123


y,



119/123


y,

Processing of a Turbine

Blade


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Blade

FPI

X-Ray

Feinguss, Wachsausschmelzverfahren, lost wax investment casting, ...Turbine Casting

Additionally: hollow geometries possible (core insertion)!

Archaeological Evidence

(Bibracte) ~ 50 B C
http://../Video/CT%20an%20Turbinenschaufeln,%20Hausherr/Turbine_Gross_Seitlich.avihttp://../Video/CT%20an%20Turbinenschaufeln,%20Hausherr/Turbine_Gross_Durchlauf.avihttp://../Videos%20f%EC%B2%A0Vorlesung/K%EC%A8%ACkan%E4%AC%A5%20in%20einer%20Turbinenschaufel.wmv


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(Bibracte) ~ 50 B.C.

cloth clip

ceramic mould filled with waxTurbine Casting

Single Crystal Casting

Metals and Alloys Bayreuth


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Metals and Alloys, Bayreuth

< 20 s

0,8...400

mm/min

Content


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a) Static

b) Cyclic (Fatigue)




7 Depending on Time: Lectures on