Anisotropic Stress Rupture Behavior of a Nickel-Base Single Crystal Superalloy

The stress rupture test was conducted to a nickel-base single crystal superalloy DD499 along [001], [011] and [111] orientations. The results indicate that anisotropic behaviors of singe crystal superalloy are significantly affected by temperature and stress level. At 760 degrees C, 790 MPa, the stress rupture property of [001] orientation is outstandingly superior to that of [011] and [111] orientations; while at 1040 degrees C, 165 MPa, the order of stress rupture is [111]>[001]>[011], but the anisotropic properties of different orientations are weakened. Fracture surface and deformation microstructure were examined by SEM. The results show that at 760 degrees C, 790 MPa, the fracture mode of [001] orientation is the combination of cleavage and quasi-cleavage; while the fracture mode of [011] orientation is pure shear due to single slip system and [111] orientation is pure shear caused by multiple slip systems. At 1040 degrees C, 165 MPa, the fracture mode of the three orientations all turns to be microvoid coalescence fracture.