Achieving specific strength-ductility synergy in lightweight Ti50(ZrNb)50-xMox refractory complex concentrated alloys: Experimental and density functional theory insights

Refractory complex concentrated alloys (RCCAs) have emerged as promising structural materials due to their high strength and compositional design flexibility. However, the inherent room temperature brittleness and high density remain primary bottlenecks restricting their engineering application. In this study, a series of non-equimolar, lightweight Ti-rich Ti50(ZrNb)50-xMox (x = 0,5,10,15,20) RCCAs were designed, all of which exhibit a single-phase body-centered cubic (BCC) structure. Among them, Ti50(ZrNb)35Mo15 alloy achieves an optimal synergy of specific strength and ductility. It displays a high yield strength of 1267 MPa and a compressive plastic strain of 23.1%. Coupled with a low density of 6.42 g cm⁻³, this results in an impressive specific strength of 197.4 MPa cm³ g⁻¹. Theoretical analysis confirms that solid-solution strengthening, predominantly stemming from the atomic size and modulus mismatch introduced by Mo additions, is the dominant strengthening mechanism. Furthermore, density functional theory (DFT) calculations show that Mo addition improves the electronic stability of the alloy by reducing the density of states at the Fermi level. Combined partial density of states, charge density difference, and bond length analyses further indicate that Mo promotes stronger interatomic interaction, which contributes to the enhanced elastic moduli and supports the optimized strength–ductility balance of the alloy.