Coercivity enhancement of hydrogenation disproportionation desorption recombination Nd-Fe-B powders by grain boundary diffusion process using Tb70Cu15Al15 alloy

•The coercivity of powders diffused with Tb70Cu15Al15 powders increased from 1074.3 kA/m to 1424.4 kA/m.•The irreversible flux loss of the powder was only 50% of that of the original HDDR powders.•The effects of diffusion conditions on the coercivity and core–shell structure of HDDR magnetic powders were investigated.•The effect of the core–shell structure on coercivity was investigated by experiments and micromagnetic simulation. The hydrogenated disproportionation desorption recombination (HDDR) Nd-Fe-B powders mixed thoroughly with Tb70Cu15Al15. The samples were subjected to a grain boundary diffusion process using various heat treatment conditions. The results show that the coercivity of the magnetic powders is significantly influenced by the diffusion conditions. Under the optimum treatment process, the coercivity of treated powders increased from 1074.3 kA/m to 1424.4 kA/m. Furthermore, the irreversible flux loss of the treated powders was also dramatically decreased by 50% at 150 °C for 100 hrs, demonstrating a significant improvement in temperature stability. The nanoscale core–shell structure leading to a notable improvement in magnetic properties was observed using transmission electron microscopy (TEM). Micromagnetic simulations were used to explain how diffusion processes affected the properties of magnetic powders.