Lightweight anomalous eutectic Al21Ti21V16Ni21Co21 high entropy alloy with superior thermal stability

A novel dual phase Al₂₁Ti₂₁V₁₆Ni₂₁Co₂₁ lightweight high entropy alloy (LW-HEA) with a density of 6.19 g/cm³ was successfully synthesized by vacuum induction melting in a relatively large form of bulk 10 kg ingot, and its thermal stability was tested by exposures at temperatures up to 1100 °C. The as-cast alloy with an anomalous eutectic structure consisting of Ni-Co-Al-Ti-rich Heusler-like L2₁ phase and V-rich BCC phase with precipitates distributed in the latter, exhibited a hardness of 578 HV, yield stress, ultimate compressive stress and strain to failure of 1417 MPa, 2312 MPa, and 13.7%, respectively. After heating, the alloy preserved both phases with their initial composition, general microstructural features, and showed nearly 100% retention of initial mechanical properties. The excellent performance is attributed to the synergistic strengthening mechanisms including hetero-deformation induced strengthening and inhabitation of dislocation movement. The excellent strength of as-cast Al₂₁Ti₂₁V₁₆Ni₂₁Co₂₁ alloy and the strength retention after thermal exposures show that its service temperature limit is superior to most HEAs and conventional superalloys developed for high-temperature applications.