Magnetic performance and microstructure of NdFeB sintered magnet by diffusing Tb10Pr90-(Cu,Al,Ga) alloys

Commercial NdFeB sintered magnets were processed by grain boundary diffusion process with serial Tb10Pr90-x(Cu,Al,Ga)x (at%) alloys, in order to study the influence of rare earths and non-rare earth metallic elements proportion change on the diffusion effect for alloy diffusion sources with low Tb content. The coercivity increased significantly from 14.20 kOe to 24.10 kOe, 25.46 kOe and 25.36 kOe respectively for the diffused magnets treated with Tb10Pr80(Cu,Al,Ga)10, Tb10Pr60(Cu,Al,Ga)30 and Tb10Pr40(Cu,Al,Ga)50. However, the coercivity optimization effect deteriorated drastically when the total amounts of metallic elements (Cu, Al and Ga) in diffusion resources reached 70 at%. Microstructure analyses demonstrated that the remarkable coercivity enhancements achieved by the relatively low metallic content sources were mainly attributed to the excellent diffusion effects, in which the Tb diffusion depths were rather deeper and the core-shell structures were easily distinguishable. Meanwhile, due to certain differences in thermodynamic characteristics and diffusion behaviors for these serial of diffusion sources, the effective introductions of Tb and Pr from the original coated sources to the inner of the magnets were respectively different. Especially, the utilization rate of Tb obtained an optimum value of 94.74% using Tb10Pr60(Cu,Al,Ga)30 alloy and the utilization rate of Pr reached the peak value of 81.76% in the use of Tb10Pr40(Cu,Al,Ga)50 alloy, providing experiment support for the further design of alloy diffusion sources with low Tb content. In addition, in-situ magnetic domain observation for the typical diffused magnets in this work was carried out to study the demagnetization behavior and coercivity mechanism of the magnet.