KINETICS OF MICROSTRUCTURAL DEVELOPMENT IN NANOCRYSTALLINE MATERIALS

A quantitative determination of the microstructural evolution resultin g fi om nucleation and growth of a primary phase is yielded. Recently developed kinetic models constitute a powerful tool when an appropriat e physical description of the growth mechanisms which drive the proces s is implemented. To account for the high grain density developing in nanocrystalline materials, diffusion controlled growth with soft impin gement has been modeled. Comparison between computed microstructures o btained with hard and soft impingement shows that the latter explains the delay of the transformation observed experimentally. Application t o the nanocrystallization of a Fe-Si-B-Cu-Nb amorphous alloy (FINEMET) is presented. The observed kinetic evolution of both transformed frac tion and microstructural quantities agree with computed values when so ft impingement is considered. The influence of the annealing temperatu re on the resulting volume and surface grain size distributions is dis cussed. (C) 1997 Acta Metallurgica Inc.