Deduction of activation energy for diffusion by analyzing soft impingement in isothermal solid-state precipitation

An analytical treatment of soft impingement has been developed for solid-state precipitation in an isothermal process following the basic assumptions (i.e., a two-stage transformation including a site saturation of nucleation, an isotropic growth and a linear concentration gradient in front of the precipitate/matrix interface). Based on the analytical treatment for soft impingement, a new approach for deducing activation energy for diffusion Q was proposed. The isothermal recipe was mainly determined by two parameters, i.e., the mean size of the second phase rf and the starting time for soft impingement t1. The method has been successfully applied to deduce Q for isothermal transformations in Al-0.2 wt.%Sc alloy and Fe-0.24C-0.93Mo alloy.