Materials, transformation temperatures & strength Olson and Hartman,

Materials, transformation temperatures & strength Olson and Hartman,

Materials, transformation temperatures & strength Olson and Hartman, 1982 Olson and Hartman, 1982 Olson and Hartman,

1982 Diffusionless transformation? Martensite can form at very low temperatures. Martensite can grow very rapidly. No composition change during transformation.

Irrational: why? Kurdjumov-Sachs-SachsSchs (011) || Nishiym-SachsWssermn (111)

(011) || [110] [101] [111]

[110] [111] [011] [011]

[111] <001> <011> <001>

[111] (111)

[101]

Orientation relationships: irrational athermal transformatio n Glissile interface

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.

50 mm general invariant-plane strain simple shear

uniaxial dilatation s s d

1 1 d 1 s=0.26

d=0.03 s d c r 1

Christian, body-centred cubic cubic close-packed b3

a3 a2 b2 b1 a1 (a)

(b) BAIN STRAIN (c) Body-centered tetragonal austenite

(d) Body-centered cubic martensite [001] b b'

[100] o a' a b (a)

o (b) b' a,a' RB

z w P1 Austenite w Observed

shape, wrong structure y x z

x (a) w P2 y z

Martensite (wrong shape) x (b) y

(c) LATTICE -INVARIANT DEFORMATION w Twin Boundary

w z x y Twinned

Martensite x z y Slipped Martensite

Correct macroscopic shape, correct structure transformation twins (Wayman) hexagonal close-packed cubic close-packed

z w P w Observed shape,

correct structure 1 Austenite y x

z x (a) y (b) Brooks, Loretto and Smallman, 1979

T 1

T 1 Ae1 To Ae3

Carbon Concentration + strain Free Energy a

x x x

Carbon Concentration

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