The application of convergent-beam electron diffraction to the detection of small symmetry changes accompanying phase transformations II. Recrystallization of superalloys

Abstract

This paper gives an example of the application of convergent-beam electron diffraction (CBED) to the detection of subtle changes in the ordering of precipitate phases which may accompany the passage of a recrystallization interface. This alteration in the ordered state of the γ phase in one nickel-base superalloy is shown not to involve any change in composition but rather the redistribution of the atomic species with respect to the atomic sites in the precipitate phase, leading to a higher degree of ordering than is normally associated with γ′. A tetragonal distortion is induced by this ordering, and it is shown that this may also influence the subsequent precipitation of cooling γ′ in the matrix. A mechanistic interpretation, based on the reactions occurring in the moving grain boundary which forms the recrystallization interface, is presented.