Tailoring the secondary orientation and creep property of single-crystal blade by designing a square spiral grain selector

As one of the primary failure modes of single-crystal (SX) blade, the creep property is greatly affected by secondary orientation. The random secondary orientation of SX blade results in large drift interval of service life. Therefore, highly efficient control the secondary orientation to enhance service life of SX blade holds paramount importance. In this paper, a square spiral grain selector was designed to achieve above goal. The geometric parameters (pitch length and wax wire diameter) and pulling rate for this selector were predicted by using ProCAST&CAFÉ model. Then, three SX blades with different secondary orientation (0°, 30°, 70°) controlled by this selector were prepared by directional experiment. With the aid of electron backscatter diffraction (EBSD) characterization, it was found that this selector can control the deviation between the secondary orientation and the specified direction within a range of 5°. The grain selection mechanism of this selector was characterized by EBSD and OM, which is dominated by the “competitive growth driven by horizontal heat flow” and supplemented by the “geometry restriction mechanism”. The creep property of SX blade was determined through plate samples, and demonstrating the significant secondary orientation dependence.