Slip activity in molybdenum single crystals compressed at 77 K

High-purity single crystals of molybdenum of five different orientations were compressed at 77 K to plastic strains between 3% and 4% to investigate the initial stage of plastic flow in these metals. Electron back-scatter diffraction was used to determine the sample orientations before and after deformation to quantify the magnitude and direction of lattice rotation. The slip trace analysis on two perpendicular faces of each prismatic specimen, made using the Nomarski interference contrast, reveals that the slip morphology depends strongly on the orientation of the applied load. The sample oriented near the axis and that of the centre-triangle orientation exhibited sharp slip traces on and planes, whereas the samples oriented near the edge of the triangle yielded by macroscopic slip on a series of high-index planes. The orientations of observed slip traces were compared with theoretical predictions of slip activity of the twelve slip systems made by the Schmid law and using the effective yield criterion developed previously using molecular statics simulations of an isolated screw dislocation under stress.