Abstract
Mechanical twinning governs the plastic deformation in ceramic materials at low temperatures. However, its mechanism is not well known because of lack of direct observations during twinning. We investigated dynamic behavior of mechanical twinning in sapphire (α-Al_2O_3) by in situ nanoindentation in a transmission electron microscope. Our in situ observations revealed that slip motion of many strain contrasts on a twin plane. This suggests that the mechanical twinning occurs by slip of twinning dislocations. However, the observed behavior of twinning dislocations may not be consistent with the double cross-slip mechanism, which is the mainstream twinning mechanism in sapphire.
