MICROSTRUCTURAL EVALUATION OF PRIMARY CRYSTALLIZATION WITH DIFFUSION-CONTROLLED GRAIN-GROWTH

A model has been developed for evaluating grain size distributions in primary crystallizations where the grain growth is diffusion controlle d. The body of the model is grounded in a recently presented mean-fiel d integration of the nucleation and growth kinetic equations, modified conveniently in order to take into account a radius-dependent growth rate, as occurs in diffusion-controlled growth. The classical diffusio n theory is considered, and a modification of this is proposed to take into account interference of the diffusion profiles between neighbor grains. The potentiality of the mean-field model to give detailed info rmation on the grain size distribution and transformed volume fraction for transformations driven by nucleation and either interface-or diff usion-controlled growth processes is demonstrated. The model is evalua ted for the primary crystallization of an amorphous alloy, giving an e xcellent agreement with experimental data. Grain size distributions ar e computed, and their properties are discussed.