Materials, transformation temperatures

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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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Diffusionless transformation?
Martensite can form at very low
temperatures. Martensite can grow very
rapidly. No composition change during
transformation.
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Irrational why?
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Orientation relationships irrational
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athermal transformation
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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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s
d
c
r
1
Christian, 1957
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body-centred cubic
cubic close-packed
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b
a
3
3
a
2
b
b
2
1
a
1
(a)
(b)
BAIN
STRAIN
(d)
(c)
Body-centered
Body-centered
cubic martensite
tetragonal
austenite
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001
b
b'
100
o
a'
a
b
(a)
o
b'
(b)
a,a'
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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
Free Energy
a
ag
ga
x
x
x
Carbon Concentration
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