Effects of high entropy and twin boundary on the nanoindentation of CoCrNiFeMn high-entropy alloy: A molecular dynamics study

To study the effects of twin boundary and high-entropy on elastic-plastic behavior of high-entropy alloys (HEAs), molecular dynamics (MD) was employed to simulate the nanoindentation on single-crystal CoCrNiFeMn HEA (scHEA), twinned CoCrNiFeMn HEA (tw-HEA) bicrystal and twinned Ni (tw-Ni) bicrystal. The deformation behaviors of the three samples were then compared with each other. Simulations revealed that the load-drop phenomenon during the indentation in the HEAs is not so apparent as that in the Ni. Microstructure characterization showed that a dense dislocation network was localized below the indentation pit of the HEAs. These phenomena are related to the damping spreading behavior of dislocations underneath the indenter. Through the analysis of the plastic zone underneath the indentation, it is found that the twin boundary inhibits dislocation penetration, and moreover, provides a slipping path for dislocations. The radial distribution of dislocation density proves that dislocations in the indentation of the HEAs are more concentrated than that in the traditional metals. Understanding the sluggish dislocation behavior and twin boundary effect help understand the deformation mechanisms underlying the mechanical response of HEAs.