Degradation processes in Nd-Fe-B permanent magnets

The susceptibility of Nd-Fe-B permanent magnets to oxidation and/or corrosi on makes problems not only during manufacturing, but also influences reliab ility and durability of components containing such permanent magnets, In th is a work, corrosion processes of Nd-Fe-B PMs were studied on the samples t aken from rotors of servomotors operating approximately the same time at si milar conditions. Two mechanisms of degradation in usual environmental cond itions were found - oxidation of intergranular Nd-rich phase caused mechani cal disintegration of sintered magnet body to individual grains of hard mag netic Nd2Fe14B phase and subsequent oxidation of these grains. The first st ep is of,meat importance. It was found that not only oxidation of the inter granular thin layer of Nd-rich phase contributes to the destruction of magn et, but also internal stresses arising from difference in specific volume o f this phase and oxides.