HVTEM in situ observations of dislocation motion in the oxide dispersion strengthened superalloy MA 754 Original Research Article

In situ straining experiments in a high-voltage transmission electron microscope have been performed on the oxide dispersion strengthened nickel-base superalloy INCONEL MA 754 at 1020 and 1065 K. The dislocations are pinned at the particles and bow out between them. After breaking free from the particles, the dislocations move in a viscous way. At low average dislocation velocities, the waiting time between full bow-out and detachment is larger than the time for the motion in-between the particles and the bowing-out, suggesting that the interfacial pinning mechanism is rate-controlling. At higher velocities, the waiting time is small compared to the time for bowing-out. Nevertheless, the particles impede dislocation motion due to the back stress which results from bowing. The spacings between the dispersoid particles along the curved dislocation segments, the curvature of the segments, the angles of attack as well as locally acting effective shear stress are estimated from the video recordings using the DeWitt–Koehler line tension model. The results are compared with earlier conventional post-mortem TEM data and macroscopic deformation data from the literature.