1. https://edge.edx.org/courses/MSM/M21/2013_Winter/about

9. Materials, transformation temperatures & strength

10. Olson and Hartman, 1982

11. Olson and Hartman, 1982

12. Olson and Hartman, 1982

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

15. Shape of martensite ?

17. Irrational: why?

19. Orientation relationships: irrational

20. athermal transformation

21. Creation of a bi-crystal
cut and rotate by angle q about axis normal to diagram q

23. Glissile interface

25. 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.

28. 50 mm

29. general invariant-plane straind s 1
uniaxial dilatation
simple shear
general invariant-plane strain
s=0.26
d=0.03

31. s d c r 1
Christian, 1957

33. body-centred cubic
cubic close-packed

34. The Bain strain

36. [001] b b' o
[100] a' a b
(a) o b'
(b)
a,a'

38. RB P P 1 2 (c) x w z y Martensite (wrong shape) Austenite (a) w x y z
Observed
shape,
wrong
structure P
(b) w x z y 1
Twinned
Martensite
Twin
Boundary
Correct macroscopic shape, correct structure x w z y z
Slipped
Martensite
LATTICE
-INVARIANT
DEFORMATION x w y

40. transformation twins (Wayman)

41. hexagonal close-packed
cubic close-packed

42. P 1 Austenite (a) w x y z Observed shape, correct structure (b) w x z

43. Brooks, Loretto and Smallman, 1979

45. Equilibrium transformation
Free Energy g a ag ga x x x
Carbon Concentration

46. Composition invariant transformation
Free Energy g a ag ga x x x
Carbon Concentration