Change in Gamma Prime Morphology and Dislocation Substructures of Single Crystal Nickel-based Superalloy, CMSX-4, Prior-crept at 1273 K-250 MPa with Simple Aging

The additional aging at 1273 K was done for the single crystal CMSX-4 pre-crept at interrupted the creep test at the strain of 0.01 at 1273 K-250 MPa. Changes in the γ' morphology and in the dislocation substructure at the γ/γ' interfaces with aging were investigated. The shape of γ' precipitates in CMSX-4 pre-crept specimen at the creep at the strain of 0.01, remained still cuboidal. But by employing the additional aging to this interrupted specimen the shape of γ' precipitates turned its shape to the rafted one perpendicular to the stress axis. A large number of the dislocations tangled were located at the γ/γ' interfaces. By the additional aging, these dislocations were rearranged regularly with increasing aging time. However, the decrease in the dislocation density at the γ/γ' interfaces with increasing aging time was not recognized. All dislocations at the γ/γ' interfaces were defined by the six-kinds of the Burgers vectors, irrespective to aging time. Consequently, dislocations at the γ/γ' interfaces were regarded as not the misfit dislocations, but the mobile dislocations in the γ channels, and the formation of the rafted γ/γ' structure might be correlated with the rearrangement of the dislocations.