Hierarchical structure and deformation behavior of a novel multicomponent β titanium alloy with ultrahigh strength

Abstract

Based on the general [Mo] equivalent criterion and d-electron orbital theory, a new ultrahigh-strength β titanium alloy with eight major elements (Ti-4.5Al-6.5Mo-2Cr-2.6Nb-2Zr-2Sn-1V, TB17) for industrial applications was developed. An ingot of five tons was successfully melted by thrice vacuum consumable arc melting. The microstructure and elements partitioning of different conditions were investigated systematically. The results suggest that the hierarchical structures of micro-scale first α phase (α f ), nano-scale secondary α phase (α s ), and ultrafine FCC substructures can be tailored by solution plus aging (STA) heat treatment. The lateral and epitaxial growth of α f phase promotes the HCP-α to FCC substructure transformation with the help of elements partitioning during the aging process. Moreover, the element V, generally regarded as β stabilizer, is found to mainly concentrate in the Al-rich α f phase in this study probably due to its relatively lower content and the strong bonding energy of Al-V. The hierarchical structure has a strong interaction with dislocations, which contributes to achieve a superhigh strength of 1376 MPa. In addition, the plastic strain is partitioned in the multi-scale precipitates (such as the α and FCC substructures) and β matrix, resulting in a considerable plasticity. TEM observation demonstrates that high density entangled dislocations at interfaces and mechanical twins exist in the STA sample after tensile test. It can be deduced that both dislocation slipping and twinning mechanisms are present in this alloy. Therefore, TB17 alloy can serve as an excellent candidate for structural materials on aircrafts that require high strength and lightweight. • A novel β titanium alloy with ultrahigh strength of 1376 MPa was developed. • The multi-scale hierarchical structures were tailored by heat treatment. • The transformation from HCP-α to FCC-substructure was observed. • The V element mainly concentrated in the micro-scale α lath.