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

In situ straining experiments in a high-voltage transmission electron micro scope have been performed on the oxide dispersion strengthened nickel-base superalloy INCONEL MA 754 at 1020 and 1065 K. The dislocations are pinned a t the particles and bow out between them. After breaking free from the part icles, the dislocations move in a viscous way. At low average dislocation v elocities, the waiting time between full bow-out and detachment is larger t han the time for the motion in-between the particles and the bowing-out, su ggesting that the interfacial pinning mechanism is rate-controlling. At hig her velocities, the waiting time is small compared to the time for bowing-o ut. Nevertheless, the particles impede dislocation motion due to the back s tress which results from bowing. The spacings between the dispersoid partic les along the curved dislocation segments, the curvature of the segments, t he angles of attack as well as locally acting effective shear stress are es timated from the video recordings using the DeWitt-Koehler line tension mod el. The results are compared with earlier conventional post-mortem TEM data and macroscopic deformation data from the literature. (C) 2001 Acta Materi alia Inc. Published by Elsevier Science Ltd. All rights reserved.