Microstructural characterization of dislocation movement during creep in powder metallurgy FGH96 superalloy

The dislocation movement during creep in FGH96 superalloy was investigated through microscopy examination. Following the increase of creep residual strain, the dislocation density increased dramatically. Both the γ' precipitate and γ-matrix were sheared by dislocations, which resulted in a large number of stacking faults across the whole grain. The detailed structure of one-layer faults and three-layer faults were analyzed in detail, which revealed the formation process of microtwin in FGH96 superalloy. The enrichment of Ti and dilution of Al in the central of microtwin were found through STEM. Further research from the atomic-scale had been performed, which showed that Al was substituted by Ti and formed a "γ'-like" linear complexions. The substitution process was performed during the atom-reordering after γ' precipitate sheared by three 1/6 < 112> type partials. The microtwin traversed the whole grain but was pinned at the Σ3 twin boundary, and the interaction between microtwin with Σ3 twin boundary were systematically studied as well. HR-TEM observation showed that the gliding direction and plane of partial dislocations were different from that of Σ3 twin, which resulted in the strengthening effect of Σ3 twin on creep deformation. There were nearly 60 % Σ3 twin boundaries in FGH96 superalloy and this might be a significant aspect of strengthening of the material.