Abnormally enhanced displacement burst at elevated temperatures of AZ31 magnesium alloy during nanoindentation

The unveiling of temperature effects on the deformation behaviors of wrought magnesium (Mg) alloys is beneficial for optimizing the hot forming parameters of these alloys with limited room temperature (RT) formability. In the present work, we performed nanoindentations on individual grains of textured wrought AZ31 alloy along the normal direction (ND) from RT to 300 °C to investigate the intrinsic non-basal dislocation behaviors at various temperatures. Interestingly, we observed abnormally enhanced nanoindentation displacement bursts (pop-ins) at elevated temperatures ranging from 150 to 250 °C, which is beyond the general scenario that higher temperatures typically result in smoother plastic flow. The bursts exhibited Gaussian-like statistics, which differ from the well-reported bursts with power-law size distributions resulting from the destruction of jammed dislocation configurations. Through transmission electron microscopy (TEM) examination of the microstructure beneath the indentation just after the burst, we found that the abnormal displacement bursts originated from the heterogeneous nucleation of prismatic screw 〈a〉 dislocations due to the exhaustion of dislocation sources within the specified temperature range.