An atomic-scale insight into Ni3Al slip traces

Abstract We examined at the atomic scale using in situ scanning tunnelling microscopy under ultra-high vacuum environment the slip traces left by dislocation movements at the free surface of Ni3(Al,Ta) single crystals deformed in compression at different temperatures, namely room temperature, 400 K and 600 K. The purpose is to extract from the slip traces, considered as direct signatures of dislocation movements in the bulk, the elementary dislocation mechanisms that could be at the origin of the so-called yield stress anomaly in this ordered crystallographic structure. The atomic surface structure has never been concomitantly observed with slip traces, but atomic scale resolution has been currently achieved allowing the imaging of a single lattice spacing deviation along a slip trace. Our atomic scale observations of slip traces do not permit to draw decisive conclusions regarding the various models that have been proposed to explain the yield stress anomaly, but they definitively bring new and unique insights in the understanding of this phenomenon. In particular, they show the formation and breaking of incomplete Kear-Wilsdorf configurations, which unambiguously supports interpretations of in situ TEM observations. They also prove that the so-called Kear-Wilsdorf locks are indeed early mobile on the cube cross slip plane, which is usually not accounted for in the models.