ATOM-PROBE STUDY OF THE CRYSTALLIZATION PROCESS OF AN FE73.5SI13.5B9NB3CU1 AMORPHOUS ALLOY

The crystallization process of a melt-spun Fe73.5Si13.5B9Nb3Cu1 amorph ous alloy was investigated by atom probe field ion microscopy (APFIM). It was found that Cu-rich clusters were formed in the early stage of annealing of the amorphous alloy even below the crystallization temper ature. Above the crystallization temperature, it was found that the cr ystallization of alpha-FeSi bcc solid solution occurred independently of the crystallized fcc Cu particles. In the optimum annealing conditi on, Cu enriched fcc particles containing approximately 60 at% Cu were found to coexist with the alpha-FeSi solid solution and the B and Nb e nriched amorphous phase. From these observations, it was concluded tha t the formation of Cu clusters in the early stage caused the inhomogen eity of the Fe concentration in the amorphous phase and this caused an increased density in the number of nucleation sites for the crystalli zation of the alpha-FeSi phase. Nb and B were excluded from the crysta llized alpha-FeSi phase and enriched in the remaining amorphous phase. This led to the stabilization of the amorphous phase and hindrance of the growth of alpha-FeSi grains.