Rapid-thermal-process pre-treatment promoted precipitation towards strengthening hard magnetism of Sm2Co17-type magnets

Abstract

Dislocations can act as heterogeneous nucleation sites but their annihilations upon heating sacrifice point defects nearby, weakening the driving force for precipitate nucleation. In order to keep a high density of dislocations and point defects together, here rapid-thermal-process (RTP) pre-treatment was carried out to promote the precipitate nucleation in Sm2Co17-type permanent magnets that evolve gradual formation and dissociation of dislocations during concurrent precipitation and recrystallization. As exhibited in a model magnet Sm25Co49.3Fe17.1Cu5.6Zr3.0 (wt.%) with high-density dislocations at solution-treated state, the RTP pre-treatment can induce excess point defects owing to the migration of solute atoms towards equilibrium state and the quenching of point defects, and suppress the early-stage diffusion-controlled dissociation of dislocations. After whole-process isothermal aging and slow cooling, the RTP pre-treated magnet possesses much higher fraction of hexagonal SmCo5 (1:5H) nanoprecipitates than the non-pre-treated one, giving rise to effective enhancements in coercivity Hcj from 26.20 to 30.34 kOe and in knee-point field Hk from 14.43 to 19.20 kOe. These findings add insight into controlling precipitation in dislocation-bearing supersaturated solid solutions, which are feasible for strengthening the Sm-Co-based magnets.