Morphological evolution of coherent multivariant Ti11Ni14 precipitates in Ti-Ni alloys under an applied stress -: A computer simulation study

Coherent precipitation of multi-variant Ti11Ni14 precipitates in TiNi alloys was investigated by employing a continuum field kinetic model. The structural difference between the precipitate phase and the matrix as well as the orientational differences between precipitate variants are distinguished by nonconserved structural field variables, whereas the compositional difference between the precipitate and matrix is described by a conserved field variable. The temporal evolution of the spatially dependent field variables is determined by numerically solving the time-dependent Ginzburg-Landau (TDGL) equations for the structural variables and the Cahn-Hilliard diffusion equation for the composition. In particular, the interaction between precipitates, and the growth morphology of Ti11Ni14 precipitates under strain-constraints were studied, without a priori assumptions on the precipitate shape and distribution. The predicted morphology and distribution of Ti11Ni14 variants were compared with experimental observations. Excellent agreement between the simulation and experimental observations was found. (C) 1998 Acta Metallurgica Inc.