Influence of Ta intergranular addition on microstructure and corrosion resistance of Nd–Dy–Fe–B sintered magnets

Nd–Dy–Fe–B magnets require a prolonged high temperature sintering process because of the enlarged melting point of intergranular (Dy,Nd)-rich phase, which subsequently results in abnormal grain growth of the Nd2Fe14B matrix phase. In this work, in order to achieve higher coercivity and maintain the remanence Br simultaneously, Ta was introduced into Nd–Dy–Fe–B magnets through intergranular addition. With the addition of 0.2 wt.%, the average grain size of the matrix phase was reduced from 22.4 μm to 8.7 μm, and the coercivity Hcj can be enhanced from 16.7 kOe to 17.7 kOe without sacrificing Br. It is found that Ta entered mainly into the intergranular regions and rarely located inside the matrix phase, hence hindering the abnormal growth of Nd2Fe14B grains. In addition, stability of the intergranular phase was also improved, which leads to better corrosion resistance of the magnets against both electrochemical and hot/humid environments.