A study on the corrosion behavior of the (Nd, MM)2(Fe, Co, Ni)14B-type sintered magnets

The binary powder blending technique (BPBT) was employed in production of anisotropic (Nd, MM)2(Fe, Co, Ni)14B-type sintered magnets (MM: denotes a Misch-metal). The composition of the master alloy was close to the stoichiometric Nd2Fe14B compound, while the sintering aid (SA) had a composition of MM38.1Co46.4Ni15.4. The magnets were made by blending different ratios of the master alloy and the sintering aid. The corrosion behavior of these magnets was compared with that of the Nd17Fe75B8 base alloy by potentiodynamic polarization measurements in H2SO4 solution. By decreasing the amount of Nd-rich grain boundary phases and substitution of some Fe atoms by Co and Ni, an improvement in the corrosion resistance of the magnets was observed. The Ndl1.9MM2.9Fe73.9Co3.3Ni1.1B6.9 compound exhibited the minimum corrosion rate within this investigation.