Activation of deformation twinning in ultrafine-grained high-entropy alloys via tailoring stacking fault energy and critical twinning stress

In this study, we propose a new material design approach to activate deformation twinning in ultrafine-grained (UFG) AlCoCrCuFeNiTi-based high-entropy alloys (HEAs) by considering both thermodynamic and microstructural aspects. Stacking fault energy of the solid-solution phase is reduced by tailoring composition with increasing Co/Ni ratio and diminishing the concentration of Al and Ti through precipitation. Furthermore, grain size is adjusted to enable the flow stress to surpass the critical twinning stress. It results in the activation of nanotwinning in the UFG HEAs, making the alloys exhibit high strain-hardening after yielding from 1.6 to 2.3 GPa.