Changes in electrochemical responses of some Fe-B-Si-Cu-Nb alloys before and after devitrification

Abstract

The synergistic effects of Nb and Cu on the crystallization of Fe-B-Si alloys led to a class of nanocrystalline alloys which had excellent magnetic properties (1). While Cu is supposed to accelerate the nucleation of crystallites, addition of slow diffusing components like Nb, Ta, V, and W, help in reducing grain growth and consequent grain size. The controlled annealing of Fe-B-Si-Nb-Cu is utilized to exploit the excellent magnetic properties of these alloys in the nanocrystalline state. The structural changes occurring on crystallization have been studied for these nanocrystalline alloys (2), (3), (4), (5), (6) and (7). They generally demonstrate multiple stages of crystallization. It was initially felt that the result of the primary crystallization process was a body centred cubic α-Fe phase, but there is increasing evidence now that the primary product is an ordered DO3 phase having a stoichiometry close to Fe80Si20 (4), (5), (6) and (7). The crystallization processes in these alloys involve subsequent secondary transformation of the remaining amorphous grain boundary phase to form various intermetallic compounds (2) and (6). There is some evidence that a critical concentration of Si is required for the formation of the DO3 phase 6 M. Muller, N. Mattern and L. Illgen, Z. Metallkde. 82 (1991), p. 895.(6).