Development of shear bands in f.c.c. single crystals

Abstract

Factors contributing to the formation of shear bands in f.c.c. materials have been studied in single crystals of Cu, Al and Al-3%Mg. The shear band formation within a microstructure containing mechanical twins is investigated at room temperature in Cu crystals, in which mechanical twin lamellae had been produced by predeformation at 77 K. Shear bands occurred in the crystals irrespective of orientation due to the presence of the twin lamellae. The effects of solute atoms and crystal orientations during rolling at room temperature are examined in crystals of Al and Al-Mg where no twins-are formed during rolling at room temperature. Here the occurrence of shear bands is closely correlated with the development of a layered dislocation structure, which is controlled by the geometry of slip and by dynamic recovery. It is concluded that generally the presence of a lamellar structure such as mechanical twin lamellae or layered dislocation arrangements is essential for shear band formation in f.c.c. materials during rolling, and that shear bands are not formed if the development of these layers is suppressed by dynamic or static recovery. Thus, shear banding can be considered to be a typical low temperature phenomenon.