Martensite crystallography and elastic-stiffness coefficients

We considered the effect of the elastic-stiffness coefficients on the martensite crystallographic features, especially the habit plane. We approached the problem with an elastic-energy-minimization inclusion model. As shown previously, this model agrees exactly with the WLR-BM invariant-plane-strain theories when elastic stiffness is neglected and strain energy equals zero. As a first example, we considered the large-strain Fe-31Ni (fcc to bcc) transformation. Second, we considered a small-strain example: In-23Tl (fcc to fct). Finally, we considered the A 15 compound Nb3Sn (bcc to bct), which shows soft-mode behavior during cooling, where the C' = (C-11 - C-12)/2 elastic stiffness essentially vanishes, leading to a near-zero shear modulus. All three cases yielded the same result: the habit plane shows no response to elastic softening or stiffening.