Phase-field simulation coupled with a CALPHAD database for analyzing microstructural evolution during liquid-phase sintering of Nd-Fe-B magnets

Understanding microstructural evolution during liquid-phase sintering (LPS) is crucial for enhancing the coercivity of Nd-Fe-B sintered magnets. This study developed the first framework for phase-field (PF) simulation of LPS to analyze the microstructural evolutions in real alloy systems. A phase diagram database of the Nd-Fe-B-Cu system, evaluated using the calculation of phase diagrams (CALPHAD) methodology, was integrated into the PF model of sintering to analyze sintering behaviors in multiphase and multicomponent systems. The PF simulations provided thermodynamically plausible microstructural evolution of the Fe-15Nd-6B-0.1Cu (at%) alloy. The results from these PF simulations with different initial liquid phase distributions indicated that the distribution of the liquid phase affects the densification rate but not the grain growth. This suggests that optimizing the initial distribution could enhance densification without promoting coarsening of the main phases. Additionally, simulations of LPS at different temperatures revealed that sintering temperature impacted the microstructural density and distribution of Nd-rich phases at the post-sinter annealing temperature. The PF simulation framework provides valuable insights for enhancing the coercivity of Nd-Fe-B sintered magnets.