Recombination characteristics of the Nd-Fe(-Co)-B(-Ga-Zr)-type anisotropic hydrogenation, desorption, disproportionation, recombination alloys

Abstract

The recombination characteristics of the Nd-Fe-B-type isotropic and anisotropic hydrogenation, desorption, disproportionation, recombination (HDDR) alloys were investigated using three types of alloys: alloy A (Nd12.6Fe81.4B6), alloy B (Nd12.6Fe81.3B6Zr0.1), and alloy C (Nd12.6Fe68.8Co11.5B6Ga1.0Zr0.1). Alloy A is featured with the isotropic HDDR character, while alloys B and C are featured with the anisotropic HDDR character. Recombination characteristics of the alloys were examined by observing the coercivity variation as a function of recombination time. Microstructural development during the HDDR was examined by means of transmission electron microscopy, and it was correlated with the coercivity variation. The present study revealed that the intrinsic coercivities of the recombined materials rapidly increased with increasing the recombination time and then showed a peak, after which the coercivities decreased gradually as usual. However, it has been found that the degraded coercivity was recovered significantly on prolonged recombination. Compared with the isotropic HDDR alloy A, the anisotropic HDDR alloys B and C are notable for their greater recovery of coercivity. The significant recovery of coercivity was accounted for in terms of the development of a well-defined smooth grain boundary between the recombined grains on prolonged recombination. (C) 1999 American Institute of Physics. [S0021-8979(99)57208-3].