Distinct origins of deformation twinning in an additively-manufactured high-entropy alloy

Multiple simultaneous or sequential deformation mechanisms exist at the heart of extraordinary mechanical behavior of high-entropy alloys. As additive manufacturing (or 3D printing) is changing the landscape of materials engineering, the 3D-printed high-entropy alloys evoke unmatched potential of pragmatic structure-property relationships. Uncovering such relationships demands meticulous analysis of plastic deformation pathways and the corresponding stress responses. Here we present an electron backscatter diffraction (EBSD)-based study pertaining to the tensile deformation mechanisms of a CrMnFeCoNi high-entropy alloy fabricated via laser-beam powder bed fusion (PBF-LB). The tensile deformation of the 3D-printed high-entropy alloy exhibits distinctive recurring stress drops of ∼90 MPa (∼11% of its ultimate tensile strength), spanning ∼10% of the total strain prior to failure due to the occurrence of deformation twinning. The EBSD results reveal how the onset of deformation twinning is essentially guided by crystal orientation and exhaustion of gliding dislocations. A new twinning propensity factor, defined as a ratio of the twinning Schmid factor to the slip Schmid factor of the parent grains, is proposed to reflect the tendency of deformation twinning. The twin size increases linearly with increasing twinning propensity factor. These findings shed light on the underlying deformation mechanisms and provide a theoretical guidance for developing advanced high-entropy alloys via additive manufacturing.