Coupling CALPHAD Method and Entropy-Driven Design for the Development of an Advanced Lightweight High-Temperature Al-Ti-Ta Alloy

In this study, a new lightweight Al-Ti-Ta alloy was developed through a synergistic approach, combining CALPHAD methodology and entropy-driven design. Following compositional optimization, the Al_87.5Ti_6.25Ta_6.25 (at.%) alloy was fabricated and isothermally heat-treated at 475 °C for 24 h to attain equilibrium. X-ray diffraction (XRD), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC) analyses revealed a dual-phase microstructure comprising a 50 vol.% FCC matrix enriched in Al and 50 vol.% Al₃(Ti,Ta)-type intermetallic phase (IP). Notably, the FCC phase exhibited a high-melting transition temperature of 660 °C, surpassing conventional Al-Si cast alloys. Phase-specific nanomechanical properties were evaluated using Nanoindentation. Microindentation tests demonstrated exceptional microhardness of approximately 3300 MPa. These results indicate the alloy's superior hardness compared to conventional alloys such as Al-Si (A390), 7075 Al alloy, and CP-Ti, even exceeding Ti-64 alloy at a 15% lower density. The alloy's stability under prolonged heat treatment at 475 °C, reflected by stable phases, microstructure, and mechanical properties, highlights its enhanced thermal stability, which can be attributed to entropy-driven phase stabilization. This study underscores the effectiveness of integrating entropy-driven design strategy with CALPHAD predictions for the accelerated development of advanced Al-based alloys.