Coercivity enhancement in heavy rare earth-free NdFeB magnets by grain boundary diffusion process

Abstract

Grain boundary diffusion of a Pr3(Co,Cu) eutectic alloy has been performed for coercivity enhancement on Nd-lean Nd10Fe84B6 nanocrystalline ribbons. The coercivity increases from 0.5 T to 2.5 T after 6 h of infiltration at 600 °C. High resolution electron microscopy and energy dispersive X-ray spectroscopy show that the excess α-Fe present in the initial samples diminishes during infiltration, giving rise to the formation of a Rare Earth-rich RE-Fe inter-boundary phase and a layer of (Nd,Pr)2Fe14B close to the surface of the hard magnetic grains. Such a microstructure favours the coercivity by increasing the nucleation field for reversal magnetization and providing magnetically isolated/decoupled hard grains.