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Materials, transformation temperatures & strength

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.

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Materials, transformation temperatures & strength

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  1. Materials, transformation temperatures & strength

  2. Olson and Hartman, 1982

  3. Olson and Hartman, 1982

  4. Olson and Hartman, 1982

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

  6. Irrational: why?

  7. Orientation relationships: irrational

  8. athermal transformation

  9. Glissile interface

  10. 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.

  11. 50 mm

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

  13. s d c r 1 Christian, 1957

  14. body-centred cubic cubic close-packed

  15. 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

  16. [001] b b' [100] o a' a b (a) o b' (b) a,a'

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

  18. transformation twins (Wayman)

  19. hexagonal close-packed cubic close-packed

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

  21. Brooks, Loretto and Smallman, 1979

  22. a + strain a g Free Energy a ag ga x x x Carbon Concentration

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