以扩散支配相变动力学方法为基础, 建立了多相三维流动凝固模型. 模型考虑了固、液、气三相扩散相变对Fe-Bi-Mn三元合金凝固的影响, 模拟研究了合金体系中Bi和MnS易切削相的析出过程, 并分析了易切削相的多相相变过程和多相扩散路径. 结果表明: 易切削相的析出过程受多相相变-扩散作用影响, M_ls,MnS(MnS的固-液质量相变速率)较大, MnS的分配系数大而扩散系数小, 当C^*_s,MnS(MnS的固相界面浓度)大于C_l,MnS(MnS的液相浓度)时, 液相MnS在固-液界面处浓度降低, 最终被固相完全“捕获”, 导致MnS不再富集; M_ls,Bi(Bi的固-液质量相变速率)较小且M_gl,Bi(Bi的液-气质量相变速率)为负值, Bi的分配系数小而扩散系数大, 凝固过程中存在气相Bi且C_l,Bi(Bi的液相浓度)始终大于C^*_s,Bi(Bi的固相界面浓度), 故Bi持续流动富集于MnS周围, 直至凝固结束. 研究工作将模拟结果与实验结果进行了对比, 两者吻合较好.

The solidification process of alloys are not just liquid to solid phase transformation, in fact in some alloys liquid to gas and gas to liquid phase transformation processes happen. A method incorporating the full diffusion-governed phase transformation kinetics into a multiphase volume average solidification model is presented. The motivation to develop such a model is to predict the multiple effect of inclusions precipitation behavior in castings. A key feature of this model, different from most previous ones which usually assume an infinite solute mixing in liquid lead to erroneous estimation of the multiphase diffusion path, is that diffusions in solid, liquid and gas phases are considered. Here solidification of Fe-Bi-Mn ternary alloy is examined. As MnS and Bi have large differences in the solute partition coefficient, diffusion coefficient and liquidus slope, the multiphase diffusion path shows differently from those predicted by infinite liquid mixing models. In this work, a three-dimensional mathematical model for a three-phase flow during its horizontai solidification was studied based on diffusion-governed phase transformation kinetics. Effects of Fe-Bi-Mn ternary alloy solidification on solid-liquid-gas phase transformation were considered. The free-cutting phase precipitation behavior was studied and multiphase transformation and multiphase diffusion path of free-cutting phase precipitation behavior were analyzed. Results show that the multiphase transformation-diffusion is strongly influenced by free-cutting phases precipitation behavior: MnS has a relatively large partition coefficient and small diffusion coefficient with larger M_ls,MnS (solid-liquid mass transfer rate of MnS). During solidification, C^*_s,MnS (solid interface concentration of MnS) may become even larger than C_l,MnS (liquid concentration of MnS), MnS in liquid is assumed to be fully ‘trapped’ in solid and there is no longer any enrichment of MnS; however Bi has a relatively small partition coefficient and large diffusion coefficient with smaller M_ls,Bi (solid-liquid mass transfer rate of Bi) and negative M_gl,Bi (liquid-gas mass transfer rate of Bi), during solidification, C_l,Bi (liquid concentration of Bi) always greater than C^*_s,Bi (solid interface concentration of Bi). In addition, due to the existence of Bi-gas phase, Bi continuous to flow, enriched in the solidified around MnS. Calculated results show good agreement with experimental data.