Distinguishing between slip and twinning events during nanoindentation of magnesium alloy AZ31

During the penetration of a spherical indenter, the pop-in events can be observed on the load-penetration depth curves. Catoor et al. (2013) have found the 〈a〉 type dislocations and extension twins in TEM by probing the 3.3 μm radius spherical indenter on single crystal Mg. However, in their research, they did not find when the extension twin appeared. So at present work, we solved this problem by probing a 5 μm radius indenter on selected grains of polycrystal Mg alloy AZ31. Multiple indentation tests were performed on a large [112¯0] oriented grain, and two curves with same applied load of 1.5 mN and their residual imprint are displaying in the pictogram. Curve (a) shows “yielding” event, and it is found that the basal slip is the only deformation mode observed in the AFM image. While both “yielding” and “pop-in” events are observed on curve (b). Inspection of its AFM image reveal the presence of the basal slip lines and the extension twin on the surface of the indent. This confirms that the initial yielding behavior is due to slip and subsequent pop-in is due to the onset of a twinning event.141