Rate-dependent mechanical behavior of single-,bi-,twinned-,and poly-crystals of CoCrFeNi high-entropy alloy

While considerable effort is made to understand the solid solution strengthening on the deformation behavior of high-entropy alloys(HEAs),relatively little attention is paid to the role of microstructural interfaces,especially twin boundaries(TBs),on the strain-rate sensitivity(SRS)of them.To address this,we have conducted micropillar compression experiments on single-,bi-,and twinned-crystals of Co CrFe Ni HEA and compared the results with those obtained with uniaxial tensile and compression tests on polycrystalline bulk samples.Results show that SRS,as well as the yield strength and plastic flow behavior,in single crystals are orientation dependent due to the differences in the maximum Schmid factors.While the high-angle grain boundaries arrest dislocation motion,TBs allow for dislocation transmission through them,which result in distinct mechanical responses.While the bi-crystal’s deformation behavior is controlled by the‘hard’grain,twinned crystals exhibit an‘averaged’response.The large diversity of the reported SRS values in face centered cubic HEAs could be due to the varying fractions and thus contributions of annealing twins in the tested samples.