Nanocrystallization in driven amorphous materials

The nanocrystallization of mechanically milled amorphous alloys was examined both experimentally and theoretically. Mechanical milling induces the precipitation of nanocrystals in an initially amorphous Nd-Fe-B magnetic alloy. The effects of milling speed and duration on precipitate growth/size were investigated. Milling intensity was found to significantly affect the steady-state precipitate size. Precipitate growth kinetics and steady-state precipitate size were governed by a dynamic equilibrium between defect-enhanced diffusional precipitate growth and impact-induced crystal attrition. A linear decrease in steady-state precipitate size with increasing milling speed was predicted, consistent with our experimental data. Nanocrystallization in many driven amorphous alloys can be understood using the kinetic model developed here.