1. 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

2. Materials, transformation temperatures & strength

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

4. Shape of martensite

6. Irrational: why?

8. Orientation relationships: irrational

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

11. Glissile interface

13. 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.

16. 50  m

17.  s 1 s 1  1 uniaxial dilatation simple shear general invariant-plane strain s=0.26  =0.03

19. c r  s 1 Christian, 1957

21. body-centred cubic cubic close-packed

22. (a) BAIN STRAIN (c) Body-centered tetragonal austenite (d) Body-centered cubic martensite a a a 1 2 3 b 3 b 1 b 2 (b)

23. [100] [001] o a a' b b' o b a,a' (a) (b)

25. 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 wz y P 2 Martensite (wrong shape)

27. transformation twins (Wayman)

29. Two non-coplanar invariant- plane strains q p d e

30. The Bain Strain (F B F) where F is an orthonormal basis parallel to the unit cell of austenite

31. Assume that the lattice invariant deformation is on the system

32. u deformed to x by (F B F)

35. lattice invariant deformation is

36. h deformed to l by (F B F)