Investigating spatio-temporal deformation in single crystal Ni-based superalloys using in-situ diffraction experiments and modelling

Abstract

In this study, we perform a detailed analysis of room temperature deformation of a [100]–orientated single crystal Ni-based superalloy, CMSX-4 micropillar, using a combinatorial and complimentary characterisation approach of micro-Laue diffraction coupled with post-deformation microscopy and crystal plasticity modelling. Time-resolved micro-Laue data indicated that deformation was initiated by activation of multiple slip (after 5% engineering strain) which led to the generation of a plastic strain accumulation accompanied by a two-fold increase in the dislocation density within the micropillar. Subsequent to that, slip occurred primarily on two systems (11¯1)[101] and (111)[1¯01] with the highest Schmid factor in the single crystal micropillar thereby resulting in little accumulation of unpaired GNDs during a major part of the loading cycle, upto 20% strain in this case. Finite element crystal plasticity modelling also showed good agreement with the experimental analyses, whereby significant strains were found to develop in the above slip systems with a localisation near the centre of the micropillar. Post-deformation transmission electron microscopy study confirmed that deformation was mediated through a/2<110> dislocations on {111} planes in the γ-phase, while high stress levels led to shearing of the γ′ precipitates by a/2<110> partials bounding an anti-phase boundary free to glide on the {111} planes. During the deformation of the single crystal micropillar, independent rotations of the γ and γ′ phases were quantified by spatially resolved post-deformation micro-Laue patterns. The degree of lattice rotation in the γ-phase was higher than that in the γ′-phase.