Superb strengthening behavior in a precipitation strengthened Co-rich CoCrNiAlTi medium entropy alloy with acceptable ductility

For metallic materials, it is challenged to enhance the strain hardening rate under uniaxial tension when high flow stress is achieved. Here, we present a strategy enabling to obtain superior strain hardening ability via fabricating an incompletely recrystallized structure in a precipitation-strengthened Co-rich CoCrNiAlTi medium-entropy alloy. It involves to introduce a low-temperature ageing process in the CoCrNiAlTi alloy experienced high-strain cold rolling process. Accompanied with the formation of the partially recrystallized microstructure, high-density band-like L1₂-type ordered phase has formed via discontinuous precipitation. During the plastic straining process, deformation twins have been triggered by the high-stress field owing to its metastable structure. As expected, the alloy demonstrates synergistically substantial strengthening and toughening effects, thus, a superb mechanical property combination with ultimate tensile stress of 2.20 GPa and ductility of over 5.0% has been achieved at ambient temperature.