Thin foils of the γ′-strengthened superalloy were strained within a transmission electron microscope, and dislocation processes in the precipitate-free zones and in the γ′-strengthened material next to them were observed under load. Because the precipitate-free zones were merely solid-solution strengthened, they were softer than the interiors of the γ′-strengthened grains. Many different slip systems were activated in the precipitate-free zones; even under relatively low external stresses. Multiple slip permitted the compatible deformation of neighboring grains. Extensive cross-slip and double cross-slip, in the precipitate-free zones, led to a high dislocation multiplication rate. Easy creation of dislocations in the precipitate-free zones, and pile-ups at the borders between the precipitate-free zones and the γ′-strengthened interiors of the grains, enhanced the propagation of slip across grain boundaries and thereby lowered the yield strength of the material.

In situ Transmission Electron Microscopy Study of Dislocation Processes at Precipitate-Free Zones in a γ′-Strengthened Superalloy. D.Baither, T.Krol, E.Nembach: Philosophical Magazine, 2003, 83[35], 4011-29