Abstract Directional composite microstructures have successfully been prepared with directional columnar crystal forms at the center and equiaxed crystals with Ti2AlC particles at the edge of sample. Microstructure evolution, influenced by different solidification rates, is discussed and forming mechanisms of this composite microstructure have been revealed. Results show that the primary phase of α is observed from 60° of the primary dendritic arms, and β is from 90°. When the drawing velocity increases from 0.2 to 1.1 mm/min, the width of the columnar crystal decreases from 1.95 to 0.61 mm, and the distance between growth sites of Ti2AlC and most edge of the sample decreases from 1.04 to 0 mm. Obviously, the solid-liquid interface forms with low solidification rate. Forming the Ti2AlC phases consumes Ti the in local area, and the α primary phase forms with more than 49.4 at. % Al. The change of solidification rate has no effect on the concave shape of the solid-liquid interface because the influence of the drawing rate cannot change the influence of the heating power on the thermal balance of the molten pool. Ti2AlC particles move to the skin layer with the melt flow during directional solidification. This leads to a decrease in the heterogeneous nucleated particles near the centre of molten pool, to guaranteeing the growth conditions necessary for large columnar crystals.

中文翻译：

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CCDS TiAl基复合材料中Ti2AlC颗粒分散及不同凝固速率柱状晶形成的研究

摘要 已成功制备了以定向柱状晶为中心、等轴晶与Ti2AlC 颗粒在样品边缘的定向复合微结构。讨论了受不同凝固速率影响的微观结构演变，并揭示了这种复合微观结构的形成机制。结果表明，α 的初级相是从初级枝晶臂的 60°观察到的，而 β 是从 90°观察到的。当拉拔速度从 0.2 增加到 1.1 mm/min 时，柱状晶的宽度从 1.95 减小到 0.61 mm，Ti2AlC 生长点与样品大部分边缘的距离从 1.04 减小到 0 mm。显然，固-液界面形成时凝固速率低。形成 Ti2AlC 相会消耗局部区域的 Ti，α 初级相形成于 49.4 at 以上。%铝。凝固速率的变化对固液界面的凹面形状没有影响，因为拉深速率的影响不能改变加热功率对熔池热平衡的影响。Ti2AlC 颗粒在定向凝固过程中随着熔体流动移动到表层。这导致熔池中心附近的异质成核颗粒减少，以保证大柱状晶体所需的生长条件。Ti2AlC 颗粒在定向凝固过程中随着熔体流动移动到表层。这导致熔池中心附近的异质成核颗粒减少，以保证大柱状晶体所需的生长条件。Ti2AlC 颗粒在定向凝固过程中随着熔体流动移动到表层。这导致熔池中心附近的异质成核颗粒减少，以保证大柱状晶体所需的生长条件。