HRTEM/STEM CHARACTERIZATION

1
AFOSR MEANS2 Working Meeting
HRTEM/STEM CHARACTERIZATION
Outline
Microstructure of 0.2 crept (tension) Rene104

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

Microstructure of 2 crept (tension) Rene104

• Examination of structure of thicker twins

2
ISOLATED FAULTING

• One of the feature of the 0.2 deformed
  microstructure
• Not as prevalent as the SF on a different (111)
  slip plane
• Faulting observed predominantly in the ?
  precipitates

OBSERVATIONS

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

100 nm
3
DETAIL OF THE ISOLATED FAULT ENDING AT THE ???
INTERFACE
110
A
C
B
SESF
C
A
C
B
A
4
THE INTERFACE DISLOCATION ANALYSIS
Probe Deconvoluted
Nye Tensor ??? ?
Moire Fringe
Schematic
MD Simulation
Shear Strain
Ni3Al
Ni
A?
??
A?
?B
zonal?C?
5
HOW DO ISOLATED FAULTS FORM?
??
A?
??
??
1)
CSF
Zonal partial C?
A?
A?
SESF
A?
??
A?
??
ISF
ISF
SESF
??
??
A?
2)
??
ISF
??
SESF
Zonal partial C?
ESF
A?
ESF
ISF
A?
ISF
6
ISOLATED FAULT ANALYSIS

• Stronger intensity in the SESF (heavier elements
  gt partitioning)

• Stronger indication of Ordering

• Confirmation of SESF or CSF not possible

7
ISOLATED FAULT ANALYSIS
(-1-11)
(111)
8
STACKING FAULT ANALYSIS IN THE MATRIX

b1/6 112_at_30
ISF
b-1/6 112_at_30
ISF
9
EXTENDED FAULTS
10
MICROTWIN STRUCTURE LAYER FAULTING AT THE
INTERFACE
Rene 104, 677ºC 690MPa 2.0 Strain
1/6lt112gt pairs
14 atomic planes
11 atomic planes
11
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)

TTW_8_16
F_TTW_8_16

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

Energy comparison (Super-cell energy 0K)
TTW
DO24
TTW_8_16 -416.07eV F_TTW_8_16 -416.22eV
TTW
TTW
DE -0.15eV/cell
The DO24 fault translates into decreasing the
energy by -96.5mJ/m2.
12
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)

TTW_8_16
F_TTW_8_16

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

Energy comparison (Super-cell enthalpy)
TTW
DO24
TTW_8_16 -349.19eV F_TTW_8_16 -349.06eV
TTW
TTW
DE 0.13V/cell
The DO24 fault translates into increasing the
energy by 83.5mJ/m2.
13
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)

TTW_Pa1_19
TTW_Pn1_19

• 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 ).

?
PTW
Energy comparison (Super-cell energy 0K)
TTW
TTW
TTW_Pa1_19 -414.36eV TTW_Pn1_19 -414.28eV
DE 0.08V/cell
The fault translates into increasing the energy
by 51.5mJ/m2.
14
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)

TTW_Pa1_19
TTW_Pn1_19

• 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 ).

?
PTW
Energy comparison (Super-cell energy 0K)
TTW
TTW
TTW_Pa1_19 -492.76eV TTW_Pn1_19 -492.75eV
Energetically the same!
15
EXTENDED FAULTS
2x 1/6112
16
OUTCOME AND FUTURE PLANS

• ISOLATED FAULTING (UNDERSTANDING THE MECHANISM)
  gt 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