Research Digest 17To validate the developed PF model, a PF simulation using hypothetical ternary system with elements A, B, C was performed. A CALPHAD database of the A-B-C system used in the previous study [2] was also used for this simulation. In the computational domain, 50 spherical solid particles and 50 liquid phases are randomly arranged, and the outer areas of them were set to be gas phase. The initial distribution of the solute components was assumed to be uniform. The interfacial energy Fig. 1. Time evolution of the phases and solute components during the LPS. The black lines indicate surfaces of the solid particles and grain boundaries.References 1) T. T. Sasaki, T. Okubo, K. Hono, Acta Matar. 115, 269-277 (2016). 2) W. Villanueva, K. Grönhagen, G. Amberg, J. Ågren, Comput. Mater. Sci. 47, 512-520 (2009). 3) H. Ravash, L. Vanherpe, J.Vleugels, N. Moelans, J. Eur. Ceram. Soc. 37, 2265-2275 (2017).the solid-solid, solid-liquid, solid-gas, and of liquid-gas interfaces were σs-s = 0.8 J/m2, σs-l = 0.4 J/m2, σs-g = 0.795 0.4 J/m2, and σl-g = 0.791 J/m2, respectively [2]. Figure 1 shows the evolution of the phases and solute components. The macroscopic densification of the solid compacts occurred through solid-state bonding, while the liquid phases penetrated the solid-solid interface due to the interfacial energy balance. The distributions of the solute components changed as predicted from the CALPHAD database. These results demonstrate that the developed PF model can analyze not only the macroscopic densification of the sintered compact, but also the phase transformation and solute diffusion based on the CALPHAD database in the multiphase and multicomponent system. Therefore, our developed PF model is expected that it will provide valuable information for realizing microstructure to improve the coercivity of the Nd-Fe-B sintered magnets by using the actual CALPHAD database of the material.1. Outline of ResearchNd-Fe-B sintered magnets are one of the strongest permanent magnets, finding applications in traction motors for electric vehicles. The coercivity of the magnets is improved by partially substituting Nd in the Nd2Fe14B phase with heavy rare earth elements such as Dy. However, the natural resources of them are limited. Therefore, heavy rare earth elements-free Nd-Fe-B magnets with high coercivity are demanded.The magnetic properties, including the coercivity, of the Nd-Fe-B sintered magnets can be improved by controlling their microstructure [1]. The microstructure of the Nd-Fe-B sintered magnets is strongly affected by morphological changes and solute diffusion during the liquid-phase sintering (LPS) in their fabrication process. Therefore, predicting the microstructural evolution during liquid-phase sintering and acquiring key factors to control the microstructure will improve the coercivity of Nd-Fe-B sintered magnets.Numerical simulation using the phase-field (PF) method is an effective approach to predict the microstructural evolution during sintering. PF method is a powerful numerical simulation methodology for solving mesoscale free-boundary problems involving complex interface evolutions. To date, some PF models of LPS have been proposed [2, 3]. However, to the best of our knowledge, no PF model can simultaneously analyze macroscopic densification occurring in sintering and solute diffusion in multiphase and multicomponent systems. Moreover, no PF simulation has been performed to predict LPS of Nd-Fe-B sintered magnets. The purpose of this study is to predict the microstructural evolution during LPS of Nd-Fe-B sintered magnets and to identify the key factors for realizing the microstructure that improves their coercivity. T0 this end, a novel PF model of LPS is developed in this study. The developed PF model can provide thermodynamically reasonable simulation results by coupling it with the thermodynamic database of the Nd-Fe-B system obtained by the calculated phase diagram (CALPHAD) method. In fiscal year 2022, which is the first year of this study, we developed a new PF model of LPS that can simultaneously analyze multiple phenomena during LPS: densification, grain growth, phase transformation, and multicomponent solute diffusion based on CALPHAD database.2. Research ActivitiesPhase-field Modeling of Liquid-phase Sintering of Nd-Fe-B sintered MagnetsAkimitsu ISHII
元のページ ../index.html#19