Phase Transformation and Magnetic Properties of Mechanically Alloyed PrCo5-based Magnets

PrCo5-based nanograin PrxCo100-x (x=14～22) alloys with high coercivity were synthesized by mechanical alloying and subsequent annealing. The crystallization, phase components and magnetic properties of the alloys were investigated systematically. The main phase of the alloy for x=14 is Pr2Co17 with rhombohedral Th2Zn17-type. The amount of the Pr2Co17 phase decreases with increasing Pr content, and a nearly single phase PrCo5 with hexagonal CaCu5-type is formed in Pr19Co81 alloy. Further increase in the Pr content leads to the formation of another magnetically hard Pr2Co7 phase with its Curie temperature about 350℃.Remanences decrease monotonously with increasing Pr content, whereas the coercivities increase, reaching a maximum of 2040 kA/m (25.6 kOe) in Pr19Co81 powders milled for 5 h and annealed at 973 K for 2 min,and then decrease for higher Pr content. The high coercivity is attributed to the high anisotropy field of the PrCo5 phase and its nanoscale grain size.