The strength-ductility balance of Al0·4CoCu0.6NiTix (x≤1.0) and Al0·4CoCu0·6NiSi0.2Tix (x≤0.5) high entropy alloys by regulating the proportion of Ti and improving the cooling rate

The work prepared Al0·4CoCu0·6Ni(Si0.2)Tix (Si0Tix (x ≤ 1.0) and Si0.2Tix (x ≤ 0.5)) high entropy alloys (HEAs) with high strength and excellent plasticity by optimizing the added ratio of Ti and rapid cooling, discussed the effects of Ti and cooling rate on HEAs' microstructures and mechanical properties. The results showed that arc melted and copper injected Si0Tix HEAs' phase structures changed gradually from “fcc + L12 (Si0Ti0.25)” to “fcc + L12+minor bcc (Si0Ti0.5)” and finally to “fcc + L12+bcc + Ni3Ti-type phase (Si0Ti0.75, Si0Ti1.0)”. But they transformed from “fcc + L12+bcc + Ni16Ti6Si7-type phase (Si0·2Ti0.25)” to “fcc + L12+bcc + AlNi2Ti-type + Ni16Ti6Si7-type phase (Si0·2Ti0.5)” for Si0.2Tix HEAs. The micro-hardness of arc melted and copper injected HEAs gradually increased compared with Si0Ti0 matrix HEA and that of copper injected HEAs were larger than arc melted HEAs (except Si0Ti0.5). The compressive properties of Si0Ti0.25, Si0Ti0.5 and Si0·2Ti0.25 HEAs were relatively better, in which, the yield strengths of copper injected Si0Ti0.25, Si0Ti0.5 and Si0·2Ti0.25 HEAs were 2.7, 2.9 and 4.8 times than that of arc melted Si0Ti0 matrix HEA (295 MPa), the fracture strain rates of the corresponding HEAs were 47.1%, 22.4% and 13.5% respectively. It introduced three strengthening mechanisms of solid solution strengthening, trace phase transformation and fine grain strengthening and realized HEAs' strength-ductility balance.