Effects of B or C addition on phase transformation and magnetic properties of Pr17Co83−xTx (T = B or C, x = 0-10) alloys prepared by mechanical alloying

Effects of B or C addition on phase transformation and magnetic properties of Pr17Co83−xTx (T = B or C, x = 0-10) alloys, prepared by mechanical alloying and subsequent annealing, have been studied systematically. The X-ray diffraction results show that after annealing at 650 °C for 2 min, the main phase of Pr17Co83 alloy is a crystalline PrCo5 phase with hexagonal CaCu5-type structure. The Pr2Co14B phase with tetragonal Nd2Fe14B-type structure appears when the B content increases. The formation of the Pr2Co14B phase is also confirmed by observing its spin reorientation transition temperature Tsr (= 390 °C) on ac susceptibilities versus temperature curves. The amount of the Pr2Co14B phase increases with increasing B content. Further increasing the B content leads to the formation of another magnetically hard PrCo4B phase with hexagonal CeCo4B-type structure with its Curie temperature about 190 °C. In the Pr17Co73B10 alloys, PrCo4B phase becomes the main phase. Remanences decrease monotonously with increasing B content, whereas the coercivities increase, reaching a maximum of 17.9 kOe in Pr17Co81B2 powders milled for 5 h and annealed at 650 °C for 2 min, and then decrease for the higher B content. In the case of C addition, however, the alloys are composed of a mixture of a major PrCo5 phase and secondary Pr2Co17 and PrCo2Cx phases. No expected Pr2Co14C phase has been observed in all of the C-containing powders. The magnetic properties of the C-containing alloys have not been improved evidently.