KINETIC-THEORY OF MICROSTRUCTURAL EVOLUTION IN NUCLEATION AND GROWTH-PROCESSES

Macroscopic properties of materials are highly dependent on their micr ostructure. In materials obtained by a phase transformation the comple te knowledge of microscopical parameters, such as mean radius and grai n size distribution, is essential to tailor properties of technologica l interest. A kinetic theory is presented, based on the same assumptio ns as the Kolmogorov-Johnson, Mehl-Avrami (KJMA) formulation; that is to say, randomly distributed active nucleation sites that grow isotrop ically until collision gives rise to growth stop at the grain boundari es. The theory is an extension of KJMA because it evaluates probabilit ies of impingement between grains, giving actual grain size population s as a function of time. The formalism allows us to model arbitrary de pendencies of the kinetic parameters (nucleation and growth rates) on macroscopic and/or microscopic variables, and on time. The theory has been tested against Monte Carlo simulations, showing that it is quanti tatively exact in its predictions of the grain size populations. Speci fic dependencies on the kinetic parameters have been studied in order to understand the growth behavior of real materials. In particular, in terface and diffusion controlled growth are studied, and differences i n the final grain size distribution and related parameters are discuss ed. (C) 1997 Elsevier Science S.A.