对流扩散-多相相变体系内柱状晶/等轴晶形成过程的数值模拟

采用扩散支配相变动力学方法对Fe-Bi-Mn系易切削合金侧向快速凝固过程进行数值研究。建立对流扩散-多相相变体系三维凝固模型,考虑固、液、气三相扩散流动相变对合金凝固的影响,模拟研究合金中MnS和Bi(易切削相)的柱状晶/等轴晶形成过程。结果表明:合金凝固过程中MnS和Bi的柱状晶/等轴晶形成模式强烈受对流扩散和多相相变影响;对流扩散为正值处,溶质的多相质量相变速率较大且富集程度较低,流动稳定易形成柱状晶;对流扩散为负值处,溶质的多相质量相变速率较小且富集程度较高,当晶尖处溶质富集到一定程度,对流扩散与多相相变产生的紊流使柱状晶尖端断裂,成为等轴晶形核中心,此处为等轴晶稳定形成区域。

Numerical Simulation of Columnar Crystal/Equiaxed Crystal Formation Model in a Convection Diffusion-multiphase Transformation System

The horizontal rapid solidification of Fe-Bi-Mn free-cutting alloys were simulated by using diffusion-governed phase transformation kinetics.The three-dimensional solidification model for a convection diffusion-multiphase transformation system was built.Effects of alloys solidification on solid, liquid and gas phases flow diffusion transformation were considered.The Bi and MnS (free-cutting phases) of alloy columnar crystal/equiaxed crystal formation process were simulated.The results show that columnar crystal/equiaxed crystal formation model of Bi and MnS in alloy solidification is strongly influenced by convection diffusion and multiphase transformation terms;the large multiphase mass transfer rate and small enrichment degree of species easy to form columnar crystal where the convection diffusion term is positive;the small multiphase mass transfer rate and large enrichment degree of species appear at where the convection diffusion term is negative, the tip of columnar crystal breaking is caused by turbulence from convection diffusion and multiphase transformation when the species enriched to some degree, and which becomes the nucleation center of columnar crystal and the equiaxed crystal continues to grow and tends to be stable.