Microstructure and strengthening mechanisms in multi-phase Ni₃₆Co₃₀Cr₁₁Fe₁₁Al_12-xTa_x high entropy alloy

Recent studies indicated that single face centered cubic (FCC) phase high entropy alloys (HEAs) are insufficiently strong for engineering applications. Multi-phases Ni₃₆Co₃₀Cr₁₁Fe₁₁Al_12-xTa_x (x = 2, 4, 6, 8, 10 at.%) HEAs are designed to obtain higher strength and ductility. The mechanical properties, phase formation and strengthening mechanism of Ni₃₆Co₃₀Cr₁₁Fe₁₁Al_12-xTa_x alloys are investigated. The results suggest that the alloy consists of FCC phases, ordered face centered cubic (L1₂) phases and Laves phases. Laves phases exist with the Ta content increasing from 2% to 10%, and the volume fraction is changd from 0.14% to 31.02%. The phase predicted factors suggest that the addition of Ta promotes the production of Laves phases. The yield strength and total strain of Ni₃₆Co₃₀Cr₁₁Fe₁₁Al₈Ta₄ high entropy alloy are 892.77 MPa and 21.18%, respectively. L1₂ phases can be observed in the alloy. The strength mechanism of multi-phases Ni₃₆Co₃₀Cr₁₁Fe₁₁Al_12-xTa_x high entropy alloy is mainly the precipitation strengthening.