Unveiling the coordinated mechanism of orientation and grain boundaries on tensile deformation in directional solidification gas turbine blades

Since the misoriented grains in directional solidification blades can significantly degrade their mechanical properties, the anisotropy of DZ411 nickel-based superalloy during tensile testing along the solidification direction at 650 °C was investigated. The experimental samples were directly extracted from gas turbine blades. In single crystals (SX), as the orientation deviation angle increases from 2° to 14°, the yield strength decreases from 996 to 871 MPa. The yield strength of bi-crystal (BX) exhibits greater sensitivity to the orientation deviation angle. For the BX sample with deviation angles of 5° and 7° (5,7), the yield strength is 987 MPa. However, when the orientation deviation angles increase to (4,16), (24,32), and (20,28), the yield strength declines to 708, 701, and 688 MPa, respectively. Electron backscatter diffraction results reveal that orientation rotation is dominated by the {111}〈110〉 slip system during tensile deformation, and the rotation direction of the grains can be influenced by adjacent grains. Additionally, grain boundaries (GB) constrain orientation rotation, as the strength at the GB exceeds that within the grain, causing the slip bands to stop moving near the GB. At the same horizontal position, the farther from the GB, the greater the orientation change. The primary reason for the elongation degradation in BX is the difficulty in coordinating the rotation directions during deformation due to the orientation differences between the two crystals.