ICYS Annual Report 2023Nd-Fe-B sintered magnets are one of the most powerful permanent magnets in practical applications, such as traction motors for electric vehicles. The coercivity of the Nd-Fe-B magnets is strongly affected by their microstructure [1]. To enhance the coercivity, the small crystal grains of the Nd2Fe14B phase must be covered with a thin grain boundary phase. Generally, Nd-Fe-B magnets are produced by liquid-phase sintering (LPS). The microstructure morphology and crystal grain size are predominantly determined during LPS. Therefore, predicting the microstructural evolution during LPS and acquiring key factors to control the microstructure are crucial for improving the coercivity of Nd-Fe-B sintered magnets.The phase-field (PF) method is a powerful numerical methodology for predicting the microstructural evolution during sintering. To simulate macroscopic densification of the sintered compact, the rigid-body motion of the sintered particles must be considered. Although several PF models of sintering have been proposed [2], no PF model can simultaneously analyze the macroscopic densification induced by the rigid-body motion, phase transformation, and solute diffusion in multiphase and multicomponent systems. Moreover, PF simulations of microstructural evolution during LPS of Nd-Fe-B magnets have never been conducted.This study developed a new PF model of LPS in multiphase and multicomponent systems to investigate the microstructural evolution during LPS of Nd-Fe-B magnets. The developed PF model can simulate the densification of the sintered compact by considering the rigid-body motion. In addition, the PF model provides thermodynamically reasonable simulation results by coupling it with the thermodynamic database obtained by the calculated phase diagram (CALPHAD) method. Before investigating the LPS of Nd-Fe-B magnets, the developed PF model was validated [3]. The validation was conducted using a CALPHAD database of a hypothetical ternary system with elements A, B, and C. Figure 1 shows the microstructural evolution during the PF simulation of LPS. The rigid-body motion-induced densification, liquid phase evolution, and grain growth/coarsening were simultaneously analyzed. The liquid phases penetrated grain boundaries: this behavior is known as “rearrangement” in LPS. Figure 2 shows the changes in the concentration distributions of the A, B, and C elements. These changes are reasonable and consistent with those predicted from the CALPHAD database. From these results, the developed PF model demonstrated that it is a promising simulation model to predict the microstructural evolution during sintering in multiphase and multicomponent systems. Therefore, the PF model will produce valuable insights for enhancing the coercivity of Nd-Fe-B magnets through some PF simulations obtained Research Digest Akimitsu ISHII1. Outline of Research2. Research ActivitiesFig. 1. Microstructural evolution obtained from the LPS simulation using the developed PF model coupled with a CALPHAD database of a hypothetical ternary system.Fig. 2. Time evolutions of the concentration distribution of the solute components A, B, and C.References 1) K. Hono, H. Sepehri-Amin, Scr. Mater. 67, 530-535 (2012). 2) M. Xue, M. Yi, Comput. Model. Eng. Sci. 140, 1165-1204 (2024). 3) A. Ishii, T. Koyama, T. Abe, M. Ode, Mater. Today. Commun. 40, 110116 (2024).using the CALPHAD database of multinary systems consisting of Nd, Fe, B, and other elements.14Multi-phase-field Modeling of Liquid-phase Sintering: Toward Predicting Microstructural Evolution of Nd-Fe-B Sintered Magnets
元のページ ../index.html#16