Indentation Pop‐in Behavior of CoCrFeNiAl_x High‐Entropy Alloy

Indentation pop‐in behavior of CoCrFeNiAl_0.1, CoCrFeNiAl_0.3, and CoCrFeNiAl_0.6 high‐entropy alloys (HEAs) at different loading rates is investigated using instrumental nanoindentation. Experimental results show that the increase in either loading rate or the aluminum atomic content (Al_x) of the alloy all have a reducing effect on the pop‐in behavior on the load–displacement curve. Meanwhile, both conditions exert a lagging effect on the triggered depth of the first pop‐in event and significantly affect the bursting width. The first pop‐in event is characterized using the previous phenomenological model and the effects of loading rate and Al_x are quantitatively analyzed through combining the elastic deformation energy prior to the first pop‐in and the energy dissipation during the indentation process. In addition, the activation volumes for pop‐in event are evaluated to be about 4–13 Ω much higher than that in pure metal, revealing the multiatom‐coordinated migration process in HEAs.