Formation mechanisms of stacking faults and twins during creep deformation of a [011] oriented nickel-based single crystal superalloy at 750 °C

The microstructure of the nickel-based single crystal superalloy CMSX-4 was investigated after [011]-oriented creep deformation at 750 °C/670 MPa. Aberration-corrected transmission electron microscopy was used to identify the types and configurations of deformation defects, such as intrinsic and extrinsic stacking faults and microtwins in both γ matrix and γ' precipitates. The findings demonstrated that the shearing of single a/3〈211〉 dislocations, which resulted from the interaction of a/2〈101〉 and a/2〈110〉 matrix dislocations at the γ/γ' interfaces, produced superlattice intrinsic stacking faults in γ' precipitates. Superlattice extrinsic stacking faults were formed through two mechanisms: successive shearing of two a/3〈211〉 dislocations on two neighboring {111} planes, and pairwise shearing of two identical a/6〈211〉 partial dislocations, which originated from two identical matrix dislocations on adjacent planes. Shearing of a/3〈211〉 dislocations dominates creep deformation, according to statistical study of the number of each type of stacking fault. Moreover, the combination of these two mechanisms resulted in the formation of deformation twins, which can shear through numerous γ channels and γ' precipitates. These results provide a further understanding of creep deformation of nickel-based single crystal superalloys at intermediate temperatures, which is essential for designing and developing novel materials.