Thermal stability of surface modified Sm2Co17-type high temperature magnets

The oxidation behavior and magnetic loss of Sm(CobalFe0.1Cu0.1Zr0.033)6.93 magnets modified with nickel coating were systematically studied. The research reveals the laws of oxidation kinetics and magnetic properties of the Ni-coated and uncoated magnets oxidized at 500°C in air. The results show that the mass gain of the uncoated magnets is 4.02mg/cm2 for 100h oxidation and 8.48mg/cm2 for 500h oxidation. As for the coated magnets oxidized at 500°C for 100h and 500h, the mass gain is only 0.06mg/cm2 and 0.22mg/cm2, respectively. The loss of remanence Br, coercivity Hcb and maximum energy product (BH)max of the coated magnets oxidized at 500°C for different time were compared with those of the uncoated magnets. The magnetic properties of the coated magnets are stable at both room temperature and 500°C, while the magnetic properties of the uncoated magnets decrease drastically. The results of scanning electron microscope and X-ray diffraction reveal the phase constitution of ordered surface oxidation zones, showing that the interdiffusion between Ni coating and the magnet is slight and Ni coating can isolate oxygen invasion and hinder Sm volatilization. These results indicate that nickel coating can protect and stabilize Sm2Co17-type high temperature magnet effectively at 500°C.