The influence of Co and Ga additions on the corrosion behavior of nanocrystalline NdFeB magnets

Abstract

Isotropic nanocrystalline Nd 14Fe 80B 6 and Nd 12Dy 2Fe 73.2Co 6.6Ga 0.6B 5.6 magnets with different grain sizes in the range of 60–600 nm have been produced from melt-spun materials by hot pressing at 700 °C and subsequent annealing at 800 °C for 0.5–6 h. The microstructure has been characterized using XRD, SEM, energy dispersive X-ray analysis, and Kerr microscopy. The corrosion behavior of NdFeB magnets has been examined on 0.1 M H 2SO 4 by in situ inductively coupled plasma solution analysis, gravimetric and electrochemical techniques. The corrosion hydrogen absorption/desorption behavior has been investigated by thermal desorption analysis and hot extraction methods. Partial substitution of Fe with Co and Ga leads to an improvement in corrosion resistance and reduces the affinity and binding energy for hydrogen in these materials. Coarsening of the microstructure results in a better corrosion performance of these materials. The corrosion behavior of the magnets in relation to phase composition, phase distribution and grain size is discussed in terms of dissolution, hydrogenation and mechanical degradation.