HRTEM/STEM CHARACTERIZATION

• Isolated faulting in ’• Intrinsic Stacking faults in the Matrix

Microstructure of 0.2% crept (tension) Rene104

Microstructure of 2% crept (tension) Rene104

• Examination of structure of thicker twins

AFOSR MEANS2 Working Meeting

Outline:

• One of the feature of the 0.2% deformed microstructureNot as prevalent as the SF on a different (111) slip plane

• Faulting observed predominantly in the ’ precipitates

100 nm100 nm

OBSERVATIONS

• Ended at the ’ interface• Ended at a SF• Transmitted through

ISOLATED FAULTING

ABC

ACBC

A

SESF

[110]

DETAIL OF THE ISOLATED FAULT ENDING AT THE ’ INTERFACE

Nye Tensor Nye Tensor Moire FringeMoire FringeProbe DeconvolutedProbe Deconvoluted

Ni3AlNi

AB

A

SchematicSchematic

zonalC

THE INTERFACE DISLOCATION ANALYSIS

MD SimulationMD Simulation Shear StrainShear Strain

HOW DO ISOLATED FAULTS FORM?

A

A

CSF

ISF

Zonalpartial=C

ISF

A

AESF

1)

2)

??

ISF

SESF

ESFA

A

SESF

A

ISF

Zonalpartial=C

ASESF

ISF

ISOLATED FAULT ANALYSIS

• Stronger intensity in the SESF (heavier

elements => partitioning) • Stronger indication of Ordering • Confirmation of SESF or CSF not possible

ISOLATED FAULT ANALYSIS

(111)(-

1-11

)

STACKING FAULT ANALYSIS IN THE MATRIX

ISFISF

ISFISF

b=1/6 [112]@30°

b=-1/6 [112]@30°

EXTENDED FAULTS

1/6<112> pairs

11 a

tom

ic

plan

es

MICROTWIN STRUCTURE LAYER FAULTING AT THE INTERFACE

Rene 104, 677ºC 690MPa 2.0% Strain

14 a

tom

ic

plan

es

TTW_8_16

TTW_8_16 = -416.07eV

F_TTW_8_16 = -416.22eV

TTW

DFT comparison of MICRO-TWIN configurations

Super-cell configurations for Ni3Ti• True Twin (8 layers), Super-cell 16 layers(TTW_8_16)• Faulted True Twin (8 layers), Super-cell 16 layers(F_TTW_8_16)

F_TTW_8_16

TTWTTW

DO24

•Both super-cells were created from a perfect L12 NI3Ti by passing 1/3 [112]. (8 partials)

Energy comparison(Super-cell energy 0K)

The DO24 fault translates into decreasing the energy by

-96.5mJ/m2.

E= -0.15eV/cell

TTW_8_16

TTW_8_16 = -349.19eV

F_TTW_8_16 = -349.06eV

TTW

DFT calculation of MICRO-TWIN configurations

Super-cell configurations for Ni3Al• True Twin (8 layers), Super-cell 16 layers(TTW_8_16)• Faulted True Twin (8 layers), Super-cell 16 layers(F_TTW_8_16)

F_TTW_8_16

TTWTTW

DO24

•Both super-cells were created from a perfect NI3Al by passing 1/3 [112]. (8 partials)

Energy comparison(Super-cell enthalpy)

The DO24 fault translates into increasing the energy by

83.5mJ/m2.

E= 0.13V/cell

TTW TTW_Pa1_19 = -414.36eV

TTW_Pn1_19 = = -414.28eV

DFT comparison of MICRO-TWIN configurations

Super-cell configurations for Ni3Al• True Twin (7 layers) with adjacent one layer pseudo-twin (TTW_Pa1_19)• True Twin (7 layers), with a fault and adjacent pseudo twin (TTW_Pn1_19)

PTW

TTW

?

•Both super-cells were created from a perfect NI3Al by passing 7x 1/3 [112] and 1x 1/6 [112] (in

case of the TTW_Pn1_19 one plane was skipped before passing the 1/6 [112] ).

Energy comparison(Super-cell energy 0K)

TTW_Pa1_19 TTW_Pn1_19

The fault translates into increasing the energy by

~51.5mJ/m2.

E= 0.08V/cell

TTW TTW_Pa1_19 = -492.76eV

TTW_Pn1_19 = = -492.75eV

DFT comparison of MICRO-TWIN configurations

Super-cell configurations for Ni3Ti• True Twin (7 layers) with adjacent one layer pseudo-twin (TTW_Pa1_19)• True Twin (7 layers), with a fault and adjacent pseudo twin (TTW_Pn1_19)

PTW

TTW

?

•Both super-cells were created from a perfect L12 NI3Ti by passing 7x 1/3 [112] and 1x 1/6 [112] (in case of the TTW_Pn1_19 one plane was skipped before passing the 1/6 [112] ).

Energy comparison(Super-cell energy 0K)

TTW_Pa1_19 TTW_Pn1_19

Energetically the same!

EXTENDED FAULTS

2x 1/6[112]

OUTCOME AND FUTURE PLANS

• ISOLATED FAULTING (UNDERSTANDING THE MECHANISM) => COMBINATION OF MICROSCOPY WORK AND PHASE FIELD)

• STEM SEGREGATION STUDIES AND AB INITIO?

• PAPERS• OBSERVATIONS OF ISOALTED FAULTING• MICROTWIN FAULTING AT THE INTERFACE AND COMPOSITIONAL EFFECTS