Lightweight, ultrastrong and high thermal-stable eutectic high-entropy alloys for elevated-temperature applications

Eutectic high-entropy alloys (EHEAs) that combine the advantages of HEAs and eutectic alloys are promising candidates for high-temperature applications. However, currently developed EHEAs still exhibit high densities and low high-temperature strengths, which limit their usage. Here we propose a strategy to design lightweight, strong, and high thermal-stable EHEAs by introducing an extremely stable Heusler-type ordered phase (L21 phase) containing a high-content of low-density elements and constructing a low lattice misfit eutectic-phase interface, which can lead to generate ultrafine and stable lamellar structures and high-density of coherent nanoprecipitates. As a manifestation of this strategy, a novel bulk Al17Ni34Ti17V32 EHEA was designed to consist of L21 and body-centered-cubic (BCC) phases (interlamellar spacing -320 nm) with a lattice misfit only 2.4%. This alloy has one of the lowest densities (-6.2 g/cm3) among all EHEAs reported previously and exhibits much higher high-temperature hardness and specific yield strengths than most reported refractory HEAs (RHEAs), lightweight HEAs (LWHEAs), EHEAs, and conventional superalloys. This work paves the way to develop light EHEAs with excellent high-temperature properties.