COMPUTER-SIMULATION OF MARTENSITIC TEXTURES

We consider a Ginzburg-Landau model free energy F(epsilon, e(1), e(2)) for a (2D) martensitic transition, that provides a unified understand ing of varied twin/tweed textures. Here F is a triple well potential i n the rectangular strain (epsilon) order parameter and quadratic e(1)( 2), e(2)(2) in the compressional and shear strains, respectively. Rand om compositional fluctuations eta(r) (e.g. in an alloy) are gradient-c oupled to epsilon, similar to- Sigma(r) epsilon(r)[(Delta(x)(2) - Delt a(y)(2))eta(r)] in a ''local-stress'' model. We find that the compatib ility condition (linking tensor components epsilon(r) and e(1)(r), e(2 )(r)), together with local variations such as interfaces or eta(r) flu ctuations, can drive the formation of global elastic textures, through long-range and anisotropic effective epsilon-epsilon interactions. We have carried out extensive relaxational computer simulations using th e time-dependent Ginzburg-Landau (TDGL) equation that supports our ana lytic work and shows the spontaneous formation of parallel twins, and chequer-board tweed. The observed microstructure in NiAl and FexPd1-x alloys can be explained on the basis of our analysis and simulations. Copyright (C) 1998 Elsevier Science B.V.