High-temperature high-entropy alloys AlxCo15Cr15Ni70-x based on the Al-Ni binary system

Abstract

To find high-temperature high-entropy alloys, a series of quaternary non-equimolar AlxCo15Cr15Ni70-x (x in atomic ratio, 0 ≤ x ≤ 35) alloys was designed, based on the Al-Ni binary system and prepared by arc-melting. The crystal structure, microstructure, and compressive properties of these alloys at both room and high temperatures were characterized. This AlxCo15Cr15Ni70-x system showed a lattice structure transition from face-centered cubic (FCC) to body-centered cubic (BCC), as the Al content was increased. In the Al content range of 12.5–19.3 at%, the L12 structured γ′ phase formed and strengthened the alloys greatly at both room and elevated temperatures. The alloy with an Al content of 19.3 at% has lamellar eutectic structure composed of γ′ and B2 phases. Due to the high γ′ phase fraction of 70 vol%, this alloy has a compressive yield strength of 924 MPa and a fracture strain of 29% at room temperature as well as good yield strength at high temperatures. Due to its high Al content, this alloy has a density of 7.25 g/cm3, 20% lower than that of the Inconel 718 alloy. At 1123 K, its specific yield strength is about twice that of the Inconel 718.