Microstructure evolution and metallurgical behavior of (Y/RE)2Fe14B sintered magnets (RE = Nd, Tb)

The magnetically hardened shells constructed by the spontaneous core–shell structure due to the enrichment of Y in the core region of (Y/RE)-Fe-B facilitate the enhancement of coercivity. In this work, we systematically compared the metallurgical behaviors of Y in R2Fe14B (RE = Nd, Tb) to investigate the modulation effect of Y on the distribution of REs in the matrix phase. During the strip casting, Y was depleted in the RE-rich phase in Y1/3Nd2/3-Fe-B while enriched in Y1/3Tb2/3-Fe-B. Under the sintering and annealing, Y was simultaneously enriched in the core of matrix phase grain, resulting in the spontaneously formation of Y-rich core and Nd-rich shell structure as well as the Y-rich core and Tb-rich shell structure. Further statistics on the concentration distribution of Y in the matrix phase indicated that the degree of aggregation for Y in Y1/3Nd2/3-Fe-B is higher than that of Y1/3Tb2/3-Fe-B, due to the different formation energy of Re2Fe14B phases. Notably, the spontaneous Y-rich core and Tb-rich shell structure demonstrates the modulation effect of Y on the distribution of Tb, inspiring an innovative scheme for construction of magnetically hardened shells.