Abstract
Abstract Here we report the synergistic effects of Zr and Dy71.5Fe28.5 (at%) co-addition on the magnetic performance of Nd-Fe-B sintered magnets and the underlying mechanism. The high-melting-point Zr suppresses the abnormal grain growth during high-temperature sintering process and also causes insufficient densification as limited by its poor wettability with the main phase grains. The co-addition of low-melting-point Dy71.5Fe28.5, however, increases the volume fraction of liquid intergranular phases upon sintering, and facilitates the formation of smooth and continuous grain boundaries, which can counteract the adverse effect of single Zr addition. As a result, the 2:14:1 main phase grains are well isolated, exhibiting an effectively weakened short-range exchange coupling between adjacent grains. Moreover, Dy diffusion towards the surface region of grains also generates a (Pr, Nd, Dy)2Fe14B magnetically hardening outer layer. Owing to the joint contributions from grain refinement, optimized grain boundary layer, and Dy-enriched hardening shell, the coercivity can be significantly enhanced from 14.0 to 21.9 kOe upon co-doping 0.3 wt% Zr and 3 wt% Dy71.5Fe28.5, accompanied with a slight remanence reduction. It demonstrates that co-doping low-melting-point and high-melting-point additives provides an efficient approach to fabricate high-performance Nd-Fe-B magnets.
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