introduction and point groups stereographic projections low symmetry systems space groups...
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Introduction and point groups
Stereographic projections
Low symmetry systems
Space groups
Deformation and texture
Interfaces, orientation relationships
Martensitic transformations
Crystallography
H. K. D. H. Bhadeshia
Martensite can form at very low temperatures.
Martensite can grow very rapidly.
No composition change during transformation.
Diffusionless transformation?
[111]
[011]
[111]
[101]
α
α
γ
γ
(011) || (111)γ α
-Kurdjumov Sachs
[111]
[011]
[111] [101]
α
α
γ
γ
(011) || (111)γ α
-Nishiyama Wasserman
[110] γ [110] γ
<001><011><001>
ααγ
Glissile interface cannot contain more than one set of dislocations.
Martensitic transformation only possible if the deformation which changes the parent into the product leaves one line undistorted and unrotated, i.e. an invariant-line.
Deformation is an invariant-line strain.
(a)
BAIN STRAIN
(c) Body-centered tetragonal austenite
(d) Body-centered
cubic martensite
a
a
a1
2
3 b3
b1 b2
(b)
Austenite
(a)
w
x
y
z
Twinned Martensite
Twin Boundary
Correct macroscopic shape, correct structure
x
w z
y
z
Slipped Martensite
LATTICE -INVARIANT DEFORMATION
x
w
y
Observed shape, wrong structure
P
(b)
w
x
z
y
1
RB
(c)
x
w z
y
P2 Martensite (wrong shape)