Grain growth effects on the corrosion behavior of nanocrystalline NdFeB magnets

Isotropic nanocrystalline Nd14Fe80B6 magnets with different grain sizes in the range of 100600 nm have been produced from melt-spun materials by hot pressing at 700 degreesC and subsequent annealing at 800 degreesC for 0,5 -6 h. The microstructures have been characterized using XRD, SEM, EDX and Kerr microscopy. The effect of grain size on the corrosion behavior of nanocrystalline magnets has been examined in N-2-purged 0.1 M H2SO4 electrolyte by in situ inductively coupled plasma solution analysis, gravimetric and electrochemical techniques and hot extraction [H]-analysis. The corrosion resistance increases with increasing grain size of the hard magnetic phase. Nanocrystalline magnets showed an increase in absorbed hydrogen by anodic polarization and abnormal dissolution by cathodic polarization. The corrosion behavior of the magnets in relation to their microstructure is discussed in terms of dissolution, hydrogenation and mechanical degradation. (C) 2002 Elsevier Science Ltd. All rights reserved.