Magnetic properties and microstructure evolution of in-situ Tb-Cu diffusion treated hot-deformed Nd-Fe-B magnets

Abstract

In this work, Tb70Cu30 alloy is employed as the addition for enhancing the hard magnetic properties of hot-deformed Nd-Fe-B magnets through in-situ diffusion. The magnets with and without Tb-Cu addition were prepared by hot pressing at 700 °C followed by hot deformation at different temperatures using melt spun Nd-Fe-B based powder as the raw materials. Tb and Cu elements were found to diffuse into the magnet after preparation. By adding 2 wt% Tb70Cu30, the coercivity and thermal stability of hot-deformed magnet were significantly improved due to the formation of local high-anisotropy (Nd,Tb)2Fe14B phase and the reduction in grain size. The intrinsic coercivity Hcj increased from 1281 kA/m to 1681 kA/m and the absolute value of temperature coefficient of coercivity |β| decreased from 0.479%/°C to 0.431%/°C for the magnets hot-deformed at 750 °C. It was confirmed that the diffused Tb atom prefers to substituting Nd in Nd2Fe14B type main phase rather than entering into RE-rich phase, and Cu distributes mainly at the grain boundaries. The reduction in crystal orientation was observed for diffused magnets, which is related to the increased rare earth-rich phase, resulting in the decreased remanence. The evolutions of the grain orientation, microstructure and magnetic properties of the magnets prepared at different hot-deformation temperatures were discussed as well.