定向凝固DZ4125柱晶高温合金晶粒生长过程组织演化及其竞争生长行为

Microstructure Evolution and Competitive Growth During Grain Growth of Directionally Solidified Column Crystal DZ4125 Superalloy

采用Bridgman定向凝固法制备DZ4125柱晶高温合金定向试棒,研究在恒定抽拉速率下定向晶粒生长过程微观组织演化及晶粒间竞争生长行为。结果表明,随着定向凝固柱晶高温合金生长高度的增加,一次枝晶间距增加,γ′相尺寸减小,且γ′相形貌由蝴蝶状向立方体状、近球状转变,枝晶间处γ′相尺寸和数量均高于枝晶干处。碳化物和γ+γ′共晶组织主要分布于枝晶间区域,且随着生长高度的增加,碳化物形貌由细小块状逐渐向条状、骨架状转变。此外,由于晶体的竞争生长,随着生长高度增加柱状晶数量明显减少,表现为在最终生长区内主要存在定向起始段中心部晶粒。上述过程主要因为存在凸固液界面生长条件,晶粒向近炉壁侧倾斜发散生长,中心部晶粒淘汰边缘晶粒发生稳定生长。

The directionally solidified column crystal DZ4125 superalloy was prepared by Bridgman directional solidification. The microstructure evolution and competitive growth of oriented crystal at a constant withdrawal rate were studied. The results show that the primary dendrite spacing increases and the sizes of the γ′precipitates decrease, as the growth height increases. The morphologies of γ′precipitates change from irregular butterfly shape into regular cube and sphere shapes, and the size and amount of γ′phase in the interdendrite are higher than those in the dendritic arm. The γ+γ′eutectics and carbides mostly distribute in the interdendritic areas and the morphology of carbides gradually changes from small block into strip or skeleton shape with the increase of growth height. Moreover, due to the competitive growth proceeding, the number of columnar crystals decrease significantly with the increase of growth height and the central grains of the initial segment are retained in the final growth zone. This is mainly due to the existence of convex solid-liquid interface, the crystals diverge towards the furnace wall and the central grains grow steadily and the edge grains are gradually eliminated.