Microstructural Evaluation of Dy-Ni-Al Grain-Boundary-Diffusion (GBD) Treatment on Sintered Nd-Fe-B Magnet

A novel GBD treatment with Dy-Ni-Al eutectic alloy powder enhanced the coercivity of the sintered Nd-Fe-B magnet plate as thick as 5mm to 1760 kA/m (22 kOe) without reducing the remanence. The results of wavelength dispersive X-ray spectroscopy (WDS) indicated that this industrially epoch-making treatment spread Dy, which is a coercivity enhancing element, from the surface to the centre of the magnet through Nd-rich phase. Microstructural observations suggested that Ni and Al, which are the melting point depressants of Nd and Dy, enabled the high diffusivity of Dy.