Achieving excellent strength-ductility balance in the lightweight refractory high-entropy alloy by incorporating aluminum

Refractory high-entropy alloys (RHEAs) have garnered widespread attention as a novel class of alloys with promising applications in high-temperature environments. However, their limited ductility has constrained their engineering application. In this study, a Ti₄₀Zr₄₀Nb₁₀Ta₁₀ base alloy with enhanced ductility was chosen, and various amounts of Al were added to investigate the microstructure and mechanical behavior of these alloys. The addition of Al aimed to trigger the cocktail effect while simultaneously enhancing the specific strength of alloys. Scanning electron microscopy and transmission electron microscopy were employed to investigate the phase composition and microstructure, revealing that the addition of Al promoted the formation of a B2 structure. With the incorporation of Al, both the yield strength and hardness of alloys increased. When the Al content reached to 8 at.%, the alloy achieved an optimal strength-ductility balance (yield strength 1030 MPa, elongation 13.4 %). The strengthening contribution was calculated and indicated that solid solution strengthening and precipitation strengthening are the two main methods. While the excellent ductility is contributed by the cross-slip of dislocations, the presence of kink bands accommodated dislocation slip and reduced stress concentration, enhancing the elongation. This study reports a system of RHEAs with excellent room-temperature strength-ductility balance, shedding light on its potential engineering applications.