CHANGES IN ELECTROCHEMICAL RESPONSES OF SOME Fe-B-Si-Cu-Nb ALLOYS BEFORE AND AFTER DEVITRIFICATION Indranil Chattoraj* and Amitava Mitra** *CRP Division and **MTC Division, National Metallurgical Laboratory, Jamshedpur, 831007, India (Received July 7, 1997) (Accepted March 31, 1998) Introduction 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 (2–7). They generally demonstrate multiple stages of crystallization. It was initially felt that the result of the primary crystallization process was a body centred cubic -Fe phase, but there is increasing evidence now that the primary product is an ordered DO 3 phase having a stoichiometry close to Fe 80 Si 20 (4 –7). The crystallization processes in these alloys involve subsequent secondary transformation of the remaining amorphous grain boundary phase to form various intermetallic compounds (2, 6). There is some evidence that a critical concentration of Si is required for the formation of the DO 3 phase (6). While the magnetic properties, crystallization kinetics and the structural changes of Fe-B-Si-Nb-Cu alloys have been studied extensively, there is very little information regarding the electrochemical behavior of these alloys. Such studies would be important for the widespread commercial utilization envisaged for these alloys, since most applications would expose the alloys to normal atmospheric environments and resultant corrosion. This investigation is an attempt at a comparative evaluation of a group of Fe-B-Si-Nb-Cu alloys as regards their electrochemical performance. This article illustrates the evolution of the electrochemical responses of the chosen alloys after exposure to different heat treatments. Thus, this investigation provides a structure - electrochemical property correlation for the soft magnetic alloys chosen for this study. The relative influence of Si, B and Nb on the electrochemical responses have been discussed in this article. The effect of the presence of the DO 3 phase is also examined. Experimental Procedures In this investigation three alloys were examined for their electrochemical behavior and structural modifications, and these had the nominal compositions shown in Table 1. These alloys were prepared by melt-spinning technique and kindly provided by Dr. P. Duhaj of the Institute of Physics, Slovak Pergamon Scripta Materialia, Vol. 39, No. 6, pp. 755–761, 1998 Elsevier Science Ltd Copyright © 1998 Acta Metallurgica Inc. Printed in the USA. All rights reserved. 1359-6462/98 $19.00 + .00 PII S1359-6462(98)00171-7 755