Mossbauer-effect study of the hyperfine field distributions in the residual amorphous phase of Fe-Cu-Nb-Si-B nanocrystalline alloys

Abstract

Amorphous Fe73.5-xCu1Nb3+xSi13.5B9 (x=0 and 1.5) alloys were isothermally heat treated at 550 degrees C in a vacuum for up to 16 h. 57Fe transmission Mossbauer spectra revealed a lower rate of crystallization for x=1.5. The annealing time dependences of the hyperfine parameters and the different behaviours of the intergranular component in both samples were studied via three-dimensional projections of the hyperfine field distributions. Segregation of Fe, Si and also B, from which the crystalline phases have been created, lead to a depletion of these elements in the residual amorphous phase. As a consequence, the number of Fe atoms with Nb, Cu and possibly B atoms in their nearest surroundings increased, giving rise to changes in the chemical and topological short-range order. The amount of the residual amorphous phase as well as its average hyperfine field decreased whereas the standard deviation of the hyperfine field distribution increased with increasing annealing time.