Effects of B or C addition on phase transformation and magnetic properties of Pr_(17)Co_(83-x)T_x (T = B or C, x = 0-10) alloys prepared by mechanical alloying

摘要

Effects of B or C addition on phase transformation and magnetic properties of Pr_(17)Co_(83-x)T_x (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 deg C for 2 min, the main phase of Pr_(17)Co_(83) alloy is a crystalline PrCo_5 phase with hexagonal CaCu_5-type structure. The Pr_2Co_(14)B phase with tetragonal Nd_2Fe_(14)B-type structure appears when the B content increases. The formation of the Pr_2Co_(14)B phase is also confirmed by observing its spin reorientation transition temperature T_(sr) (= 390 deg C) on ac susceptibilities versus temperature curves. The amount of the Pr_2Co_(14)B phase increases with increasing B content. Further increasing the B content leads to the formation of another magnetically hard PrCo_4B phase with hexagonal CeCo_4B-type structure with its Curie temperature about 190 deg C. In the Pr_(17)Co_(73)B_(10) alloys, PrCo_4B phase becomes the main phase. Remanences decrease monotonously with increasing B content, whereas the coercivities increase, reaching a maximum of 17.9 kOe in Pr_(17)Co_(81)B_2 powders milled for 5 h and annealed at 650 deg 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 PrCo_5 phase and secondary Pr_2Co_(17) and PrCo_2C_x phases. No expected Pr_2Co_(14)C phase has been observed in all of the C-containing powders. The magnetic properties of the C-containing alloys have not been improved evidently.