In situ deformation of the γ' hardened superalloy Nimonic PE16 in high-voltage electron microscopes

Abstract

In situ deformation experiments in high-voltage transmission electron microscopes have been performed on single crystals of the γ'-hardened superalloy Nimonic PE16. The accelerating voltage of the electrons was varied between 300 and 1000 kV. The configurations of paired and unit dislocations are derived from still micrographs and from images recorded on video-tape. The latter method allows one to follow the development of the configuration of individual dislocation pairs to be a function of time and space.

The main results are as follows. (1) The leading dislocation of a pair bows out strongly between the γ' precipitates and thus interacts with many of them. The spacing of the precipitates along the leading dislocation is in reasonable agreement with that derived from the Friedel relation. The trailing dislocation is nearly straight. (2) The coupling of the two dislocations of a pair is not rigid; the configuration changes as they pass through the specimen. (3) The maximum number of pairs emitted by a source is 0.8r/b, where r is the average radius of the γ' precipitates and b the Burgers vector of unit dislocations. (4) Irradiation with 1000 keV electrons affects the pinning of dislocations by γ' particles only in stressed specimens, not in specimens which have been unloaded after straining.