Dislocation substructure of single crystal nickel-base superalloy CMSX-4 creep ruptured at 1273K

To clarify the feature of the rotation of the crystal lattice in the single crystal nickel-base superalloy, CMSX-4, during the creep deformation, the crystal misorientation across the interface of gamma/gamma' phase and that misorientation in the area of the gamma and gamma' phase were investigated. Creep-rupture tests were conducted at 1273K, in the stress range of 200 to 320 MPa. Microstructural observation by SEM indicated that the cuboidal gamma' turns to the rafted one in all ruptured specimens. However, at the stresses higher than 250 MPa, the interface between the gamma/gamma' was waved, while the interface between gamma/gamma' in the specimen crept at 200 MPa remains straight one. The crystal misorientation across the interface of gamma/gamma' phase and misorientations in the area of the gamma and gamma' phase decreased with decreasing the stress. The average misorientation perpendicular and parallel to tensile directions across the interface of gamma/gamma' phase were zero, independent of stress. At the lower stress side, the cuboidal gamma' has regularly line up before rafting. However, at the higher stress side, the rafted gamma' was formed after large creep deformation, and the rotation of the crystal lattice was also large, and the cuboidal gamma' seemed to turn to the random direction. Consequently, it was suggested that the origin of the crystal misorientaiton in a single crystal nickel-base superalloy was the gamma' phase rotated by subjecting the creep deformation.