为了深入理解TiAl合金定向凝固过程中晶粒组织演化特点,采用CAFE模型(元胞自动机CA-有限元FE)模拟研究Ti-46 at.%Al合金定向凝固过程中晶粒组织形成.借助文献中微重力定向凝固实验结果验证模型.考察了形核过冷度和自然对流强度对柱状晶向等轴晶转变(CET)、晶粒尺寸、晶粒延长因子以及偏析分布的影响.模拟结果表明:降低形核过冷度可以获得完全等轴晶组织.对于完全等轴晶组织,增大流动强度会加重铸件晶间偏析,而对凝固组织形貌以及晶粒尺寸、延长因子分布无影响.增加形核过冷度,发生CET.流动强度增加导致CET延迟,促进长形晶和等轴晶混合生长,增大晶粒尺寸和延长因子以及加重偏析.CAFE模型可以被用于预测TiAl合金晶粒组织形成以及分析控制机理.%In order to deeply understand the mechanisms responsible for the grain structure evolution during directional solidification of Ti-46at.% alloy, characteristics of grain structure were simulated using CAFE model ( Cellular Automaton-Finite Element ) .CAFE model was validated by comparisons with microgravity experiments from a reference.Influences of nucleation undercooling and natural convection intensity on columnar -to-equiaxed transition ( CET ) , grain size , grain elongation and segregation were numerically investigated .Simulated results show that a fully equiaxed grain structure is obtained by lowering the nucleation undercooling .Increasing flow intensity aggravates intergranular segregation , but barely has effects on variations of grain structure morphology and distributions of grain size and elongation .With a high nucleation undercooling , CET occurs.By strengthening fluid flow, the occurrence of CET is retarded , a mixed structure of elongated and equiaxed grains is formed , both grain sizes and elongations are increased and segregation is enhanced .CAFE model can be used to predict grain structure evolution during solidification of Ti-46 at.%Al and to analyze the controlling mechanisms .
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