MEANS 2 - Li Group 李巨小组li.mit.edu/Stuff/M2/Upload/MEANS2_Fall05.pdf · Wang, Ghosh, Mills,...

MEANS 2Microstructure- and Micromechanism-Sensitive

Property Models for Advanced Turbine Disk and Blade Systems

• Program initiated February 2005

• Kick-Off Meeting in Columbus January 26-27, 2005

• Frequent updates with academic, industry and AFRL partners:- Weekly informal seminars at OSU- Weekly or bi-weekly telecons with GE and Pratt&Whitney

- STW-21 interactions with AFRL

• Personnel defined for all tasks…

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MEANS 2Microstructure- and Micromechanism-Sensitive


• Brian Tryon (GRA - MSE/UofM)• Piyush Jain (GRA - MSE/JHU)• Ray Unocic (GRA - MSE/OSU)• Clarissa Yablinsky (GRA - MSE/OSU)• Deepu Joseph (GRA - ME/OSU)• Dr. Peter Sarosi (Post-Doc - MSE/OSU)• Dr. Chen Shen (Post-Doc - MSE/OSU)• Collaborators:- B. Wang (GRA on STW-21 - MSE/OSU) - Dr. Subramanian Karthikeyan (Post-Doc - MSE/OSU)

Personnel



Processing Properties

AFOSR-MEANS 2Microstructure- and Micromechanism-Sensitive




?Microstructure

Processing Properties





Understanding ofMicromechanical

Processes:Experiment + Modeling

Microstructure



RCA-1Microstructure-Sensitive

Property ModelingGhosh, Daehn, Williams,

Whitis, Savage

RCA-2Micromechanisms and

Experimental ValidationPollock, Mills, Hemker, Flores, Larsen

RCA-3Quantitative Microstructure

Characterization and ModelingWang, Ghosh, Mills, Simmons

RCA-4Defect-Level ModelingLi, Wang, Dimiduk, Rao

Research Concentration Areas (RCAs):



20

40

60

80

100

120

140

160

180

1050 1150 1250 1350 1450 1550

Temperature (°F)

Stre

ss (k

si)

Rene 88 (Coarse)Rene 88 (Fine)Rene 104

Updated Creep Mechanism Map for Disk AlloysRene 88 (Coarse)Rene 88 (Fine)Rene 104

Dislocation BypassDislocation Bypass

1/2 <110>

1/2 <110>

MicrotwinningMicrotwinning

1/2 <110>

1/6 <112>

Isolated FaultingIsolated Faulting

1/2 <110>

Dislocation LoopingDislocation Looping

Tertiary γ’ DissolutionTertiary γ’

DissolutionTertiary γ’Tertiary γ’

APB Coupled ShearingAPB Coupled Shearing

Extended FaultsExtended Faults

Creep Mechanisms for Rene104

•• Microtwins viewed in the edge on orientationMicrotwins viewed in the edge on orientation•• Observed at intermediate temperaturesObserved at intermediate temperatures

•• Extend across entire grains Extend across entire grains -- dominant mechanismdominant mechanism

-200

200

T T

111111

677677°°C/690MPaC/690MPa

(111)

1 nm

∆

From DARPA-AIM ProgramRene88 (DARPA-AIM)Viswanathan, et al. (2004)

Mechanism forThermally-Activated Microtwinning

Orthorhombic

Reordering1

2

Ni

Al

Cubic (L12)

CSF

1/6<112>pairs

Twin

CSF

Matrix (L12)GBSource

• Swapping of atom positions to recreateL12 structure (Kolbe, 2001)

• Conservative process requiring local, closed-circuit diffusion

• Provides qualitative explanation fortemperature/time dependence of process

Microstructure Parameters:

Obtain from direct TEM measurements

Key Model Parameters:Obtain from modeling

and transient creep experiments

tptptptwin vbργ =

tp

pttertiary

frictiontertiaryeff

bf γ

τ

ττττ

⋅=

−−=

3

Velocity for Diffusion-Mediated Glide of Partials

Assumptions:• Energy penalty due to twin decreases exponentially with time

• Shear of secondary γ’ thermally assisted • Shear of tertiary γ’ is athermal• Effective stress driving shear ofsecondary γ’ is given by:

Strain Rate:

EAM calculations(Voter & Chen

potential)

Matrix (L12)

Twin

−⋅

−⋅⋅=

).()(

ln2

22

tttpeff

ttpttpordtp fb

fx

bDv

γτγγ

Energy of the 2-layer pseudotwin

Energy of the 2-layer true twin

ttttpt tKt γγγγ +−−= ).exp()()(

Monte Carlo EAM simulations of reordering suggest an exponentialdrop in fault energy with time akin to first-order reaction

RCA-4: Reordering Kinetics

Microstructure Parameters:

Obtain from direct TEM measurements

Key Model Parameters:Obtain from modeling

and transient creep experiments

tptptptwin vbργ =

tp

pttertiary

frictiontertiaryeff

bf γ

τ

ττττ

⋅=

−−=

3

Matrix (L12)

Twin

RCA:1 Mean-Field Creep Model for Microtwinning

Assumptions:• Energy penalty due to twin decreases exponentially with time

• Shear of secondary γ’ thermally assisted • Shear of tertiary γ’ is athermal• Effective stress driving shear ofsecondary γ’ is given by:

Strain Rate:

−⋅

−⋅⋅=

).()(

ln2

22

tttpeff

ttpttpordtp fb

fx

bDv

γτγγ

Effect of spatial correlation of precipitates to be considered. . .

Model parameters:Temp. = 977K

Stress = 482 MPa

γpt = 700 mJ/m2

γtt = 20 mJ/m2

Dord = 3.7x10-20 m2/sρtp = 1.6x1011/m-2

f2 = 0.34 0.38 f3 = 0.06 0.02

• Initial predictions encouraging, particularly at low strains• Provides a reasonable description of the kinetics of the

microtwinning process

Preliminary Model Predictions for Rene104

Approximate coarsening

kinetics

RCA-4

1 hour 2 hours 4 hours 8 hours 16 hours50nm

Initial Coarsening Kinetics Study(RCA-3)

•Negligible dissolution rate for coarse tertiary (30 nm) and secondary (240 nm) γ’ precipitates and volume fraction after isothermal ageing at 1500oC from 0 - 16 hours

Proprietary heat treatment from a forged disc followed by an isothermal age at 1500oF for:

However for fine tertiary γ’ precipitates (10nm) the dissolution rate is appears faster

100hrs 200hrs

Aged at 1500oF

No tertiaries No tertiaries

• EFTEM indicates complete dissolution of tertiary γ’ during ageing at 1500°F for <100 hours. Suggests that smaller tertiary γ’ dissolve more rapidly (Gibbs-Thompson).

• Complementary phase field simulations to be conducted.

Initial

Pseudobinary Phase Field vs. Experiment

0

5

10

15

20

25

0 5 10 15 20 25time (h)

mea

n pa

rtic

le ra

dius

(nm

)

simulationexperiment

800°C

0

2

4

6

8

10

12

0 10 20 30 40time (h)

mea

n pa

rtic

le ra

dius

(nm

)

simulationexperiment

760°C

Wen, Menon and Simmons

Length and time scales need to be calibrated to experiment- Interface energy -> length scale- Effective diffusivities -> time scale

Aging of Ni-23.3Cr-16.5Co-4.3Al-1.2Ti:

Secondary γ’

γ’/γ interface

PFZ Tertiary γ’ precipitates

Initial Results from 3D Atom Probe Analysis

0

50

100

150

200

0 5 10 15 20 25 30

CrNi

Num

ber o

f ato

ms

Distance (nm)

3D visualization of γ’ using an isoconcentration map at 12at.%Cr

Concentration profile across a γ/γ’ interface

γ’ γ γ’

20nm

• Validation of the thermodynamic multicomponent database

• Phase field can naturally capture the diffuseness of the interface

• 3D atom probe analysis provides calibration for:- Phase field model- EFTEM imaging of precipitate size

Sarosi, Miller and Mills

20

40

60

80

100

120

140

160

180

1050 1150 1250 1350 1450 1550

Temperature (°F)

Stre

ss (k

si)




1/2 <110>

1/2 <110>


1/2 <110>

1/6 <112>


1/2 <110>






Transition in Mechanism withMicrostructure Scale (Cooling Rate)

Coarse Structure:•1/2<110> matrixdislocations•Isolated Faulting

Fine Structure:Microtwinning

200 nm200 nm200 nm

Coarse Structure (75°F/min)

121 ksi at 1200°F0.5% Strain

• 1/2<110> dislocations in matrix

• g200 points away from bright outer fringe

• Faults are Superlattice Extrinsic Stacking Faults

(SESFs)200 nm

top

bottom

200

Mechanism of Isolated Faultingof Secondary γ’

Mechanism of Isolated Faultingof Secondary γ’

• Also requires reordering of two-layer CSF to lower energy SESF

αC Dα

ISF ISF SESF

αC Dα αC Dα

2Dα

Bαloop

DααC

CSF SESF SESF

Dα

CSF

CSFSESF

Dα

Dα

1/2<110>Dα

Dα

Modeling Isolated Faulting

ISF SESF

αC Dα

CSF

Dα

Dα

∆G* = ∆F * 1−fobsˆ k

p

q

Pslip = exp −∆G *kT

• Microtwinning being modeled as viscous process:

• Isolated faulting may be a discrete release process:

• Phase field DD modeling being used to explore energetic barriers for various hypothetical scenarios:

15 nm

M

CSlipped γ-matrixUnslipped

γ-matrix

Unslipped γ'

Pseudo-twin/SESF

(111)Requiresreordering

CSF

0 10 20 30 40 50-8

-6

-4

-2

0

2

4

0 20 40 60 80 100 120-4

-3

-2

-1

0

1

2

(×10

.46

eV)

∆E=21.7 eV∆E=16.6 eV

“M” “C”

C

M

∆E=17.4 eV

Barriers for heterogeneous nucleation:

Relaxed core

Unrelaxed core

Unrelaxed core

• Even the lowest barrier (∆E=16.6eV) has ~190 kBT (@T=1000Kelvin) !• Other shearing scenarios being explored. . .

Phase Field Dislocation Dynamics

Exploring Alternate Scenarios

Chemical reordering lowers the effective γ-surface (Echemical) of SESF configuration

-100

0

100

200

300

400

500

600

0 0.5 1 1.5 2

CSF SESF

Pseudo twin

η

mJ/

m2

VASP/MGSF for Ni3Al

Shen, Li, Wang

-1

0

1

2

3

4

5 10 15 20 25 30 35 40

(×10

.46

eV)

Unrelaxed (τ=0)

Unrelaxed (τ=700MPa)

Relaxed (τ=0)150kT

210kT

470kT

R/d (d=2.07Å)

1024d ~ 205 nm

CSF(111)

SESF

γ’Homogeneous Nucleation

BarriersShen, Li, Wang

• Reduced barrierheights due to:- Immediate reordering- Applied shear stress- Relaxed dislocationconfigurations

• Barrier heights reducedbut still too large. . .

<110> viewing direction

Layer ALayer B

Ni

Unfaulted crystal

Projected passage of two Shockley partials

Two layer CSF SESF

Pseudotwin True twin

REORDERS TO

Ni/Al

• Initial analysis indicates a two layer CSF with partial reordering towards an SESF

• Simulation of an SESF after reordering

• HRTEM image simulation of a two layer CSFbefore reordering

• Superlattice (100) fringe contrast can be used to determine the nature of the stacking fault

Exploring Reordering Process via HRTEM

20

40

60

80

100

120

140

160

180

1050 1150 1250 1350 1450 1550

Temperature (°F)

Stre

ss (k

si)




1/2 <110>

1/2 <110>


1/2 <110>

1/6 <112>


1/2 <110>






Creep Mechanisms for Rene104704704°°CC

724MPa724MPa

CSFSESFαD

αD

αB B

D Cα

Dissociated a/2<110> dislocations: 2αD

CD

αBCD

Rene88DT: 400°F/min 128 ksi

Tension-Compression AsymmetryWhitis, Henry, Viswanathan, Mills

Tension-Compression AsymmetrySondhi, Dyson and Maclean (2004):

Explain by invoking a compressiveinternal stress in the γ matrix

Source presumed to be from lattice misfit between γ and γ’

Internal stress evolves with creep strain and aging as particles become semi-coherent:

Is this approach justified based on observed substructures?

Tension-Compression Asymmetry

200 nm

100 nm

• Completely different mechanisms operative!- Dislocations in compression- Microtwins in tension• Confirm for Rene104 as fucntionof stress and temperature

Whitis, Henry, Viswanathan, Mills

Sondhi, et al(2005)

T-C Asymmetry and Orientation Anisotropy• Single crystal growth (Pollock-UM)• Microsample preparation and testing (Hemker-JHU)

• Deformation mechanisms via FIB+TEM (OSU and JHU)

• Essential input for Crystal Plasticity Models

Rene88

4mm5.6 mm7 mm

Grown in Crystallox at U. Michigan

Growth of Rene104 Single Crystals

Transverse-sections (chromic acid electrolytic etch)φ=7mm φ=5.6mm φ=4mm

100 µm 100 µm100 µm

• polycrystalline • polycrystalline • single crystalline• w. segregation



Jain, Hemker, Pollock

Rene104 Single Crystals

carbides

100 µm

0.050.05-Zr

0.080.09-Fe

0.0550.044-C

3.703.743.8Mo

.730.770.9Nb

2.332.342.4Ta

2.112.072.1W

3.493.623.1Ti

3.013.113.4Al

12.5212.6513Cr

20.8420.7620.6Co

51.250.950.1Ni

Single crystal

Original sample

ICP Results

Nominal compositi

onElement

• Carbide distribution

• No significant change in chemistry



• Segregation as-grown• Homogenization required

Strain Mapping ProcedureGrid sample by Au or Pt through vacuum evaporation using

inexpensive fine-scale nickel-mesh screens

Gold Source Nickel Mesh

Sample

Gold Markers

20 µm

As-deposited markers on turbine disk alloy

Marker deposition setup



Grid + Microstructure + Strain Mapεxxεyy

y

xCompressive straining along “y”



Comparison of Subsolvus and SupersolvusStrain Distributions in Rene 88

QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.

QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture.

Subsolvus, d = 4 µm

100 mm

• Compression at RT and 2% macrostrain

• Max strains 3X nominal• Strain distribution varies significantly with grain size

Supersolvus, d = 45 µm



Goals:• Strain distributions coupled with OIM data

- Tension- Compression

• Grain boundary sliding

Develop ResponseSurface for AIM

Validated CrystalPlasticity Model

Implement Mean-FieldProperty Model in AIM

MicromechanismDetermination

MicromechanicalModel Formulation

Validated CrystalPlasticity Laws

Crystal PlasticityFor Inhomogeneous

Materials

Initial Microstructure/Evolution

Regress ModelConstants vs. DKB

MicrostructureModeling/

Characterization

StrainMapping

Regress CP ModelConstants vs.

DKB

TransientExperiments

RCA- 1Microstructure- Sensitive

Property ModelingGhosh, Daehn, Williams,

Whitis, Savage

RCA- 2Micromechanisms and

Experimental ValidationPollock, Mills, Hemker, Flores,

Larsen

RCA- 3Quantitative

MicrostructureCharacterization and

ModelingWang, Ghosh, Mills, Simmons

RCA- 4Defect- Level Modeling

Li, Wang, Dimiduk, Rao

Refinement of Anisotropic

Model Parameters

Activation Pathways/Spatial Variation Effects

Single Crystal Testing/Micromechanism

Validation

Simulation of SpatialVariation in Microstructure

Developing Microstructure- and Micromechanism-Sensitive Models

Interactions with Other ProgramsQuickTime™ and a

TIFF (Uncompressed) decompressorare needed to see this picture.

MEANS2

DARPAEngine Systems

Prognosis (P&W)

NASA Propulsion 21

Disk Life Meter (GE)

ONR Dynamic 3-D

Digital Structure

Providing insight intomicromechanisms and time-dependent deformation responsein Ni-base superalloys

AFOSRSTW-21 Phase Field

Microstructure Modeling

1. Mean-field creep models:• Microtwinning (MT) mechanism (6/05)• MT + Isolated Shearing (IS) mechanisms• MT + IS + Climb By-pass (CB) mechanisms

2. Refined mean-field models:• Incorporate spatial distribution of precipitates• Include GB Sliding as parallel process

3. Crystal plasticity modeling with:• Tension-compression asymmetry• Anisotropy of creep/plasticity with orientation• GB Sliding as distinct process


are needed to see this picture.Microstructure-Sensitive

Property Modeling (RCA-1)


are needed to see this picture. Micromechanisms andExperimental Validation (RCA-2)

1. Enhance the fidelity of the mechanism map• Transitions and additional regimes

2. Transient creep tests• Activation energies and stress dependencies

3. Creep anisotropy and tension/compression asymmetry

• Single crystal production and microtensile testing4. Strain inhomogeneity at grain level

• Strain mapping

Quantitative MicrostructureCharacterization and Modeling (RCA-3)

1. Quantification of coarsening kinetics for Rene 104:• Effect of aging on various initial bimodal microstructures

2. Characterization of continuously-cooled structures:• Function of cooling rate • Interrupted cooling

3. Development of integrated rafting model:• Phase field DD and microstructure evolution• Include elastic modulus and lattice misfit, channel filling, misfit compensation and pipe diffusion

• Incorporation of dislocation climb to simulate dislocation network formation at γ/γ ’ interfaces



Calibration for STW-21phase field effort

Defect-Level Modeling(RCA-4)

1. Incorporation of deformation twinning and reordering energy pathway from ab initio into phase field model to unravel the mechanisms of isolated faulting andmicrotwinning in γ’

2. Kinetics of reordering will be studied with nudged elastic band calculations (EAM or ab initio)

3. Quantitative comparison of phase field modeling of dislocations cutting γ’ particles with the sharp-interface model currently being implemented at WPAFB.



MEANS 2 - Li Group 李巨小组li.mit.edu/Stuff/M2/Upload/MEANS2_Fall05.pdf · Wang, Ghosh, Mills,...

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