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.