Dislocation structures below a nano-indent of the CoCrNi medium-entropy alloy

Abstract

Using diffraction-contrast scanning transmission electron microscopy and molecular dynamics simulation, we study nanoindentation of a CoCrNi medium-entropy alloy. We find that the dislocation field produced can be separated into a zone of strongly entangled dislocations in the vicinity of the indenter and a zone of individual emitted loops that penetrate far from the indenter into the material interior. Comparing results obtained at 77 K and at 300 K, we observe at low temperature an increased hardness of the CoCrNi medium-entropy alloy, a higher dislocation density at the pit boundary, and more fragmented twinning boundaries indicating less twin growth.