Relation between Creep Rate during Accelerating Creep Stage and gamma Channel Thickness in Single Crystal Nickel-based Superalloy, CMSX-4

摘要

To elucidate the origin of the Onset of accelerating creep in a single crystal nickel-based superalloy, CMSX-4, the correlation between the creep rate during the accelerating creep stage and the thickness of gamma channel was investigated by using the single crystals crept at 1273K in a wide stress range of 100-400 MPa. The shape of gamma' phase and the thickness of gamma channel at the time of the onset of accelerating creep turn to different ones with decreasing the Stress. At the stress of 160 MPa, the cuboidal gamma' phase turns its shape to a rafted one. While at the stresses less than 160 MPa the rafted gamma' phase appears before the onset of accelerating creep. At the stresses higher than 250MPa, the cuboidal gamma' phase still remains. The correlation between the thickness of gamma channel, lambda _r, and the creep rate during the accelerating creep stage, d epsilon, was evaluated, and the following equation, d epsilon propor. to lambda _(gamma)~4 is proposed and confirmed in a wide stress range of 100-400 MPa, independent of the shape of gamma' phase. In addition, it was also confirmed that the radius of dislocation curvature within gamma channel of the crept specimens was proportional to the thickness of gamma channel defined by TEM. Consequently, the origin of the Onset of accelerating creep in a single crystal nickel-based superalloy was interpreted by the loss of creep resistance due to an increase in the thickness of gamma channel, lambda _(gamma).