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研究

Microstructure evolution and Competitive Growth during Grain Growth of Directionally Solidified Column Crystal DZ4125 Superalloy

摘要:

采用Bridgman定向凝固方法制备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,随着生长高度的增加,固液界面处温度梯度逐渐降低,一次枝晶间距增加。同时,γ′相尺寸随着生长高度的增加逐渐减小,且γ′相形貌由不规则的蝴蝶状向立方体状、近圆状转变。γ+γ′共晶组织和碳化物大多分布在枝晶间区域,且含量随着生长高度的增加逐渐增加。此外,由于定向凝固过程中晶粒的竞争生长,随着生长高度的增加柱状晶数量明显减少；在具有凸固液界面生长条件下晶粒表现为向近炉壁侧倾斜发散生长。

关键词:定向凝固;DZ4125合金;微观组织;竞争生长

Abstract:

The directionally solidified column crystal DZ4125 superalloy was prepared by means of Bridgman directional solidification. The microstructure evolution and the competitive growth of oriented crystal at a constant withdrawal rate were studied. The results showed that the temperature gradients of solid-liquid interface gradually decreased and the primary dendrite spacing increased, as the growth height increased. At the same time, the sizes of the γ′ precipitates gradually decreased and their morphologies changed from irregular butterfly shape into regular cube and sphere shapes. The contents of γ+γ′ eutectics and carbides, which were mostly distributed in the interdendritic areas, increased gradually. Moreover, due to the competitive growth proceeding, the number of columnar crystals decreased significantly with the increase of growth height. With the convex solid-liquid interface, the crystals diverged towards the furnace wall.

Key words:directional solidification; DZ4125 alloy; microstructure; competitive growth