Abstract Scope |
The purpose of this study is to achieve excellent strength-ductility synergy in CoCrNi medium entropy alloys (MEAs) via Al (for strength enhancement) and Si (for stacking fault energy reduction) co-doping. The co-doping effects on the microstructures, deformation mechanisms and mechanical properties of CoCrNi MEAs are investigated. CoCrNi and three (CoCrNi)<sub>97-<em>x</em></sub>Al<em><sub>x</sub></em>Si<sub>3</sub> (<em>x</em>=3, 5, 7) MEAs were fabricated using arc melting, followed by homogenization, cold rolling and recrystallization. Abundant nanotwins were observed in CoCrNiAlSi, suggesting a lower stacking fault energy of CoCrNiAlSi than CoCrNi. As the Al doping increased, CoCrNiAlSi MEAs resulted in enhanced strength, while the ductility decreased due to the precipitation of the hard yet brittle σ phase. Compared to CoCrNi MEA, (CoCrNi)<sub>92</sub>Al<sub>5</sub>Si<sub>3</sub> MEA exhibited a good combination of tensile strength and ductility. Moreover, the alloy's density was ~10% lower than that of CoCrNi, suggesting the great potential of the alloy for aerospace applications. |