Effect of Refractory Metal Substitution on Magnetic Property and Corrosion Behavior of Sintered NdFeB Magnets

Nd24Fe65.5-xRMxB0.97Tb7.0Dy1.1Co1.0Al0.2Cu0.23 (RM=Nb, Zr, Ti;x=0.2,0.4,0.6) magnets with high property were prepared by powder metallurgy process. The measurements of high temperature magnetic properties indicate that the value of α (temperature coefficient of remanence of NbFeB magnet) is obviously increased when the temperature is below 200 °C, and β (temperature coefficient of coercivity of NbFeB magnet) is well improved after iron is substituted by the refractory metal, e.g. in Nb and Ti-substituted magnets. The result of PCT test shows that the mass loss of Nb-substituted magnets is only about 0.07 mg/cm2, which indicates that the corrosion resistance is enhanced greatly in Nb-substituted magnets, but the opposite phenomenon is observed in Ti-substituted magnets. EDX results reveal that Dy could be prevented from oxidation when more than 0.2 wt% Zr or Ti is doped in the magnets.