NUCLEATION AND GROWTH-MODEL OF MARTENSITIC PHASE-TRANSITION

A two-dimensional idealized nucleation and growth (2D-ING) model is considered, in order to understand the experimental results relating to martensitic phase trasition. It is an extension of the Kakeshita model for nucleation process (Kakeshita et al. Mater. Trans., JIM, 34 (1993), 423), based on the nucleation probability derived from a nucleation barrier. We extend the Kakeshita model to an ideal growth process by introducing the concept of a dynamic embryo and a frozen nucleus. A dynamic embryo is a ''non-classical'' nucleus in the non-equilibrium state. After the size of an embryo is over a critical size, the embryo is transformed into a frozen nucleus. Domains in the low-temperature phase are assumed to develop gathering frozen nuclei. The results of a computer simulation based on the above model show the presence of an incubation time, which is one of the essential properties of the first-order phase transition, and display the cooperative formation of domains and the fractal distribution of their size. The experimental results on the kinetics of the martensitic phase transition in In-Tl alloys have been interpreted in terms of the above simulation results.