Effects of directional solidification parameters and crystal selector on microstructure of single crystal of Ni-base superalloys

Abstract

The single crystal of nickel-base super alloy is widely used for making turbine blades. The microstructure of the alloy, especially the deviation of preferred orientation of single crystal, possesses the most important effects on the mechanical properties of the blades. In this study, the single crystal ingot and blade of DZ417G alloy are prepared by means of the spiral crystal selector as well as the directional solidification method, and the effect of the parameters (i.e., the shape of samples, the withdrawal rate) and the structure of the spiral crystal selector on the formation of single crystal and the crystal orientation are investigated. This method can prepare not only the single crystal ingot with simple shape but also the single crystal blades with the complex shape, the simple with rod-shape can form the single crystal easily with a relatively fast withdrawal rate, but the blade with complex shape requires much slower withdrawal rate to form single crystal. The length of the crystal selector almost has no effect on the crystal orientation. However, the angle of selector plays an obvious role on the orientation; the selector with a smaller angle can effectively reduce the deviation of preferred orientation; the appropriate angle of selector to obtain optimal orientation is found to be around 30°and the deviation of preferred orientation is about 30° for this selector.

摘要

镍基单晶超合金由于其优异的性能, 被广泛运用于制备航空涡轮叶片。 本文采用快速凝固法 (HRS) 和螺旋选晶法相结合的办法, 通过改变螺旋选晶器的角度, 制备不同取向和形状的单晶试棒。 研究了样品形状, 抽拉速率以及选晶器结构对单晶形成及取向的影响。 结果表明: 简单棒状和复杂叶片形状的镍基单晶均可通过该技术手段获得。 同时, 棒状合金能在较快的抽拉速率下获得单晶组织, 而复杂的叶片形状则需要在较慢的抽拉速率才能获得所需的单晶组织。 选晶器的长度对于晶粒取向无影响, 但是选晶器角度对晶粒取向有很重要的影响, 小角度选晶器能减少晶粒的偏移, 很显然, 30° 是较为合适的选晶器角度。