Design of lightweight high-temperature structural materials based on Ti-Mo-Ta-Cr-Al refractory compositionally complex alloys, Part I: Phase stability and mechanical properties

This study presents the design and evaluation of Ti-rich refractory complex concentrated alloys (RCCAs) within the Ta-Mo-Ti-Cr-Al system, aiming for low density and high-temperature stability. Alloys containing 44–54 at.% Ti were synthesized and assessed for phase stability, microstructural evolution, and mechanical performance up to 1000 °C. All compositions primarily exhibit a single-phase disordered A2 structure, even after prolonged thermal exposure. A minor C15 Laves phase appears in Cr- and Ta-rich compositions, with Mo content playing a critical role in its formation. The alloys show significant plasticity at room temperature and maintain high strength at elevated temperatures. Among them, the 44Ti-20Mo-15Ta-15Cr-6Al (at.%) composition offers the best balance of thermal stability and mechanical performance at a density of (7.5 ± 0.1) g/cm³. Compared to commercial Ti- and Ni-based alloys, the designed RCCAs demonstrate superior strength retention above 570 °C, both in absolute and specific yield strength, outperforming single-phase Ti- and Ni-based alloys up to 1000 °C.