Orientation dependence of twinning in single crystalline CoCrFeMnNi high-entropy alloy

Tensile deformation behavior of the equiatomic CoCrFeMnNi high entropy alloy single crystals were studied along three different crystallographic orientations, i.e. [001], [1¯23], [1¯11], in order to reveal the orientation dependence of deformation twinning at room temperature. It was shown that initial yield behavior along these orientations is governed by dislocation slip mechanism and the critical resolved shear stresses for slip are independent of crystal orientation. Twinning starts at different strain levels after slip deformation, depending on the tensile testing orientation: in the [1¯11]-oriented crystals, twinning starts after 5% strain while in the [1¯23]-oriented crystals, it starts after about 25% strain. Deformation twinning was not detected in the [001]-oriented crystals under tensile loading. The critical resolved shear stresses for twinning are determined to be τcrtw = 110-140 MPa. Onset of deformation twinning in the [1¯11]-oriented crystals at low strain levels, together with multiple active dislocation slip systems, leads to a significantly higher strain hardening coefficient and stress for fracture in comparison with the [001]-oriented crystals, where the plastic deformation occurs only by multiple slip systems, and the [1¯23]-oriented crystals, in which the deformation mainly occurs by single slip and then twinning in one system at later stages of the deformation.