Twinning in CoCrFeNiMn high entropy alloy induced by nanoindentation

The nanoindentation tests of CoCrFeNiMn high entropy alloy prepared by mechanical alloying route have been performed. Pop-ins on loading curves have been characterized by their indentation load, depth and length. Locations of indents within the grains, grain sizes and their orientation were obtained by the Scanning Electron Microscope/Electron Back Scattered Diffraction analysis. The stress state under the indenter was analyzed by Finite Element Method simulations using von Mises plasticity. The analysis has shown that pop-in events can be attributed to twin initiation as the pop-in length can be correlated with the twin thickness. The estimated critical twin shear stress corresponds to the one measured by the tensile test when the indentation size effect is taken into account. Fine grained HEA has very close Critical Resolved Shear Stress values for slip and twinning.