Anomalous slip induced by the surface effect in molybdenum single-crystal foils deformed in a high voltage electron microscope

Abstract

A series of in situ deformation experiments in a high voltage electron microscope was carried out at room temperature and at 150 K with high purity molybdenum single-crystal foils. Several slip systems with low Schmid factors were observed to operate predominantly. Since the slip planes of these systems make large angles with the foil specimen surface, the choice of these slip systems are considered to be strongly influenced by the image force due to the free surface. The choice of the slip plane was well explained by considering the Schmid factor and a parameter which gives the strength of the surface effect (SE) in terms of the orientation of the slip direction and the slip plane with the foil surface. Thus, this result supports the SE mechanism of anomalous slip. Evidence for the SE mechanism is the observation of dislocation cross-slip from a “normal” slip plane to an “anomalous” slip plane with the aid of the surface image force which supplies kinks to the screw dislocation.