Plastic deformation of magnetically isotropic Cr single crystals compressed at 77 K

A series of compression tests at 77 K was carried out on chromium single crystals in magnetically isotropic state to investigate the slip activity during the first 2–4% of plastic strain. Macroscopic samples of 3 mm thickness were polished mechanically and electrolytically and their orientations determined before and after deformation by electron backscatter diffraction to assess the magnitudes and directions of crystal rotations. The crystals compressed in the direction close to [001] deformed primarily by slip on the most highly stressed (1‾01)[111] and (101)[1‾11] systems. Loading the crystals in the directions close to the [011]−[1‾11] edge of the stereographic triangle resulted in preferential twinning on 112111 systems. For loading in the center-triangle region, diffraction contrast imaging in TEM reveals the presence of [100] screw junctions between intersecting 1/2111 and 1/2[11¯1¯] screw dislocations. Using molecular statics simulations, we show that this junction does not break under the applied stress and moves together with the two dislocations on their common (01‾1) plane. In contrast to the prediction of the Schmid law, the slip morphology for center-triangle orientations is thus dominated by anomalous slip on the low-stressed (01‾1) plane.