The influence on heat treatment on the microstructure and magnetic properties of a (Nd_(11.9)MM_(2.9))(Fe_(73.9)Co_(3.3)Ni_(1.1))B_(6.9)-type magnet

摘要

The effects of sintering temperature, cooling rate and post-sintering annealing on the microstructure and magnetic properties of a (Nd_(11.9)MM_(2.9))(Fe_(73.9)Co_(3.3)Ni_(1.1))B_(6.9)-type magnet have been studied. The results show that the highest magnetic properties were only obtained at a narrow range of sintering temperature. Porosity was found to be minimized with increasing the sintering temperature up to 1060 deg C. Some grain growth occurred by increasing sintering temperature from 1060 deg C to 1080 deg C. Further increase of sintering temperature resulted in a significant decrease in magnetic properties due to formation of a Fe-rich pritectic phase that severely hindered the development of magnetic properties. The influence of cooling rate and isothermal annealing on the intrinsic coercivity and energy density has been studied in terms of electrical conductivity measurements. The results indicated that, a two-step heat treatment, incorporating slow cooling from the sintering temperature and isothermal annealing leads to a drastic improvement in the H_(ci) and (BH)_(max). The variation in the H_(ci) was ocmpatible with variation in electrical conductivity that confirmed the influence of residual stresses on the magnetic properties.