New Crystallography 8

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Introduction and point groups
Stereographic projections
Low symmetry systems
Space groups
Deformation and texture
Interfaces, orientation relationships
Martensitic transformations
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Materials, transformation temperatures & strength
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Olson and Hartman, 1982
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Olson and Hartman, 1982
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Olson and Hartman, 1982
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Martensite can form at very low temperatures.
Martensite can grow very rapidly.
No composition change during transformation.
Diffusionless transformation?
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Shape of martensite ?
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Irrational: why?
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Orientation relationships: irrational
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athermal transformation
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q
Creation of a bi-crystal
cut and rotate by angle q about axis normal to diagram
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Glissile interface
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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.
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c
r
d
s
1
Christian, 1957
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body-centred cubic
cubic close-packed
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(a)
BAIN 
STRAIN
(c) 
Body-centered 
tetragonal 
austenite
(d) 
Body-centered 
cubic martensite
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1
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3
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(b)
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[100]
[001]
o
a
a'
b
b'
o
b'
b
a,a'
(a)
(b)
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transformation twins (Wayman)
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hexagonal close-packed
cubic close-packed
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Brooks, Loretto and Smallman, 1979
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a
g
Carbon Concentration
Free Energy
a
x
x
x
ag
ga
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