Balancing the microstructure and chemical heterogeneity of multi-main-phase Nd-Ce-La-Fe-B sintered magnets by tailoring the liquid-phase-sintering

Retaining chemical heterogeneity of 2:14:1 grains and forming continuous grain boundaries are two critical contributions to the strong magnetism in multi-main-phase (MMP) magnets. However, the ideal grain boundary microstructure is usually achieved at the expense of weakening the chemical heterogeneity, which poses a big challenge. Here we report a versatile strategy to balance the chemical heterogeneity and microstructure of MMP Nd-Ce-La-Fe-B magnets through tailoring liquid-phase-sintering. At optimum 1040 °C sintering, MMP magnet with 27 wt% Ce–La substitution level exhibits an equivalent weight-bearing capacity to 40MGOe commercial Nd-Fe-B, which is attributed to the joint contributions from retained chemical heterogeneity, essential densification, homogeneous grain size distribution and continuous intergranular phase network with ordered Ia3¯ structure. When shifting sintering temperature Ts towards the higher or lower range, the deteriorated magnetic properties are dominated by distinct restraints. With Ts above 1040 °C, the decreased coercivity is mainly restrained by the negative role of gradual chemical homogenization and abnormal grain growth, as verified by experimental and simulated results. However, with Ts below 1040 °C, the unsatisfactory magnetic performance mainly roots in insufficient densification and discontinuous grain boundary. These advances may deepen our understanding on designing high-performance MMP magnets with balanced contributions from modified microstructure and retained chemical heterogeneity. Keywords: Multi-main-phase, Liquid-phase-sintering, Chemical heterogeneity, Microstructure