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 r_f 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.