Time-Resolved X-Ray Diffraction Studies on the Crystallization of Amorphous FeSiB-Based Alloys

The influence of separate and combined addition of Cu and Nb on the crystallization behaviour and the kinetics of Fe3Si formation in the system Fe77.5-x-ySi15.5B7CuxNby is investigated by means of X-ray diffraction. Addition of Cu decreases the thermal stability of the amorphous matrix, the microstructure after crystallization is unchanged. Nb controls the microstructure. The onset of the two crystallization stages and the chemistry of the product of the second crystallization stage are dependent upon the concentration of Nb. Combined addition of Cu and Nb is responsible for coexistence of nanocrystalline Fe3Si precipitations and the amorphous matrix over a wide temperature range. The formation of Fe3Si is described in terms of Johnson-Mehl-Avrami kinetics (JMA). The Avrami exponent n is affected by addition of Cu, between 410 and 430 °C it is reduced from 1.4 to 0.7. On addition of Nb n is found to be ≈ 1. The combined addition of Cu and Nb results in an Avrami exponent n = 0.7 independent of annealing temperature (T = 475 to 600 °C).