Topography of semicoherent γ/γ′-interfaces in superalloys: Investigation of the formation mechanism

A new method for the investigation of interfacial dislocations in nickel-base superalloys employing SEM has been recently established by the authors. The dislocations become visible because of grooves, which form in the γ/γ′-interface at the dislocation core. The groove formation mechanism was investigated by annealing/cooling experiments and creep experiments with the single-crystal superalloys SRR99 and CMSX-4. Possible forces for groove formation are discussed and their magnitude is estimated. The osmotic force, resulting from the vacancy supersaturation during quenching, was found to be the main reason for groove formation. The correlation between groove shape and Burgers vector of the interfacial dislocation is explained. The conditions required for observation of such grooves using SEM are discussed.