Abstract
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 γ channel was investigated by using the single crystals crept at 1273K in a wide stress range of 100-400 MPa. The shape of γ' phase and the thickness of γ 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 γ' phase turns its shape to a rafted one. While at the stresses less than 160 MPa the rafted γ' phase appears before the onset of accelerating creep. At the stresses higher than 250 MPa, the cuboidal γ' phase still remains. The correlation between the thickness of γ channel, λγ and the creep rate during the accelerating creep stage, ε, was evaluated, and the following equation, ε∝λ4 γ is proposed and confirmed in a wide stress range of 100-400 MPa, independent of the shape of γ' phase. In addition, it was also confirmed that the radius of dislocation curvature within γ channel of the crept specimens was proportional to the thickness of γ 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 γ channel, λγ.
