Effect of grain-boundary phases in Y- and Ce-substituted R2Fe14B sintered magnets

•Y and Ce used to reduce Nd content to 50%•The addition of Ga in Y- and Ce-substituted R2Fe14B did not improve the coercivity•Covering grains by the grain boundary phase influenced the coercivity.•Highest coercivity achieved at the ratio of Nd, Y and Ce as 50:10:40. Sintered R2Fe14B (R: rare earth element) magnets with a 50% Y- and Ce-substitution for Nd were studied with the goal of reducing the Nd content. Nd was substituted with Y to attain greater magnetization and with Ce for higher coercivity. In the composition with a Y:Ce = 1:1 substitution, a maximum energy density of 355 kJ/m3 (44.6 MGOe) was achieved with a residual flux density of 1.38 T and a coercivity of 533 kA/m. To improve the coercivity, the effect of adding Ga was investigated to introduce a R6Fe13Ga grain-boundary phase and thus achieve magnetic separation between the grains. As a result of adding 1.0–3.0 at% Ga, although R6Fe13Ga formed at the grain boundaries, the coercivity decreased due to the large magnetization of 0.3–0.5 T. The magnetization of the RFe2 grain boundary phase decreased with an increase in the Ce concentration, and fell to 0.05 T for Ce 100%. By introducing the RFe2 grain-boundary phase with an appropriate amount of Ce, a coercivity of 1063 kA/m (13.4 kOe) with a residual flux density of 1.22 T was achieved with a Ce content of 40% of the rare earth elements in a R2Fe14B sintered magnet.