Effect of compositional boundary on spinodal decomposition in Fe-Cr-Mo system by phase-field model

Phase-field ?????? ????????? ????????? ???????????? ????????? ????????? ?????? ????????? ????????? ??????????????? ????????? ????????? ????????? ???????????? ?????? ????????? ????????????. ?????? ?????? ?????? ??????????????? ???????????? ???????????? ????????? ???????????? ?????? phase-field ?????? ???????????????, ?????????, ?????? ????????? ????????? ?????? ??? ????????? ???????????? ????????? ???????????????. ?????????, ?????? ???????????? ???????????? ?????? ?????? ??? ???????????? ????????? ?????? ????????? ????????? ???, ????????? ???????????? ???????????? ????????? ????????? ?????? ????????? ??????????????? ????????????. ????????????, ??? ??????????????? 800K??? Fe-Cr-Mo ??????????????? ????????? ?????? ?????? ????????? ????????? ??? ????????? ????????? ???, BCC ???(??)??? Fe-rich ???????????? ???(??1)??? Cr-rich ???????????? ???(??2)?????? ???????????? ???????????? ????????? ????????? ?????? ????????? ??????????????? ???????????????. ?????????????????? ?????????????????? ???????????? ?????? ?????? ?????? ????????? ???????????????, ???????????? ??????????????? ????????? ????????? ?????? ???????????????. ??????????????? ????????? Cr??? Mo??? Cahn-Hilliard ???????????? ????????? ????????? ??????????????????, ??????????????? ????????? ????????? 1st order semi-implicit Fourier spectral ?????? ???????????????. ??????, Fe-40%atCr-3at%Mo, 800K??? tie-line ?????? ?????? ?????? ?????? ????????? ????????? ???????????? ???????????? ???????????????. ??? ??????, ?????? ????????? ????????? ??????????????? ?????????????????? ????????? ????????? ????????????, ???????????? ??????????????? ????????? ????????? ????????? ????????? ????????? ?????? ?????? ????????????. ??????, ?????? ????????? ???????????? ?????? ??????, ?????? ?????? ??? ????????? ?????? ????????? ??? ???????????? ?????? ??????????????? ????????? ???????????? ???????????????. ?????? ?????? ?????? ????????? ????????? ??? ????????? ????????? ???????????? ?????? ????????? ????????????, ?????? ?????? ???????????? ???????????? ???????????? ??????????????? ???????????? ????????? ?????? ???????????????. ??? ???, ?????? ????????? ?????? ????????? ?????? ????????? ???????????? ????????? ????????? ??????????????? ????????????. ?????????, ???????????? ?????? ????????? ?????? ??????????????? ??? ?????? ????????? ????????? ?????? ????????????. ???????????? ????????? ??????????????? ?????? ?????? ????????? ???????????? ?????? ????????? ?????? ???????????? ?????? ???????????????. ??? ???, ?????? ??? ????????? ????????? ?????? binodal ????????? ????????????, ???????????? ???????????? ????????? ??????????????? ????????? ????????? ??? ?????? ?????????????????? ????????????. ???????????? ???????????? ?????? ????????? ?????? ????????? ????????? ?????? ????????? ?????? ????????? ???????????? ?????? ??? ???????????? ?????? ????????? ?????? ????????? ?????????. ??????, ????????? ????????? ?????????????????? ??????????????? ?????? ????????? ?????? ?????? ????????? ?????? ????????? ????????????, ?????? ?????????????????? ??? ????????? ?????? ?????? ?????? ???????????????.Phase-field method is greatly adequate to simulate phase transformation with complex morphology, because it has an advantage that do not need to calculate position of interface. So, many researchers used phase-field method to simulate spinodal decomposition behavior and calculate it about various conditions, such as alloy system, composition and existence of defects. Although these enormous number of studies, however, effect of compositional boundary with large composition difference on spinodal decomposition behavior is rarely conducted. In this study, I investigated the effect of coexistence of two different composition areas on spinodal decomposition that BCC phase (??) decompose Fe-rich ferrite phase (??1) and Cr-rich ferrite phase (??2) in Fe-Cr-Mo ternary system at 800K. In this simulation, regular solution model was employed. And magnetic energy effect was ignored. Mobility and gradient energy coefficient values were obtained from literature. The evolution of microstructure was calculated by solving Cahn-Hilliard equation of Cr and Mo simultaneously and to reduce calculation time 1st order semi-implicit Fourier spectral method was used. At First, I simulated spinodal decomposition of some initial compositions on same tie-line. Consequently, when composition is closer the symmetric composition of miscibility gap, irregular and interconnected microstructure is obtained and when initial composition is far from the symmetric composition, spherical and isolated microstructure is obtained as like literatures reporting. Also, from the fact that simulation results agree with thermodynamic equilibrium fraction, composition and theoretical wavelength, the validity of this simulation is conformed. When the interface between two different composition areas exists in the system, the interface become a preference site of spinodel decomposition like other defects such as grain boundary or free surface. Compositional boundary makes compositional wave and it forms parallel microstructure to the interface in vicinity of the boundary. In contrast, microstructure far from interface is determined by the composition of compositional area interior. The microstructure formed by interface penetrates deep into each area if initial composition fluctuation is small. If the compositions of two area are in binodal composition region, phase transformation occur through nucleation and growth rather than spinodal decomposition mechanism. The wavelength and velocity of the compositional wave is varied by the composition of area interior. Therefore, the compositional wave has different shape on either side of the interface. Also, even though the compositions of areas are identical, if the composition difference at interface is larger, the velocity of wave will be faster. But, the final morphology of that area will not be affected.Maste