MAGNETIC AND PHASE-TRANSITIONS AND HDDR PROCESSES IN NDFEB-TYPE ALLOYS MONITORED BY ELECTRICAL-RESISTIVITY MEASUREMENTS

Magnetic and phase transitions and the hydrogenation, disproportionation, desorption, recombination process of NdFeB-type alloys have been investigated by electrical resistivity measurements. The Curie points and the temperatures of formation of the liquid grain boundary phase of Nd14.68Dy0.94Al0.62Fe76.47Nb0.5B6.79 and Nd1.56Fe74.9B8Cu1.5 have been determined and the kinetics of the disproportionation reaction under hydrogen and the recombination under vacuum at 820-degrees-C of these alloys have been studied for the first time by a technique employing in-situ measurements of the electrical resistivity. Differences in the kinetics of the disproportionation reactions in the two alloys, in which the Nd2Fe14B phase forms Fe, Nd-hydride and Fe2B, can be related to the effects of alloy composition and initial microstructure.