Microstructure evolution and deformation mechanism of α+β dual-phase Ti-xNb-yTa-2Zr alloys with high performance

Abstract

• Microstructure of the alloys is more sensitive to Nb rather than Ta. A slight difference in Nb content will affect the morphology of martensite and even induce ω phase transformation, resulting in completely different mechanical responses of the alloy. • The as-cast Ti-3Nb-13Ta-2Zr alloy shows the highest compressive strength (227 ±10 MPa), and compressive strain (74.3% ± 0.4%). • Nb and Ta content strongly affects Young's modulus and tensile properties of the alloys after rolling. The as-rolled Ti-3Nb-13Ta-2Zr alloy exhibits much lower modulus due to lower Nb content as well as more α"-martensite and β-phase, and a good combination of low modulus and high strength among all the designed alloys. Biomedical β-phase Ti-Nb-Ta-Zr alloys usually exhibit low elastic modulus with inadequate strength. In the present work, a series of newly developed dual-phase Ti- x Nb- y Ta-2Zr (wt.%) alloys with high performance were investigated in which the stability of β-phase was reduced under the guidelines of ab initio calculations and d-electronic theory. The effects of Nb and Ta contents on the microstructure, compressive and tensile properties were investigated. Results demonstrate that the designed Ti- x Nb- y Ta-2Zr alloys exhibit typical characteristics of α+β dual-phase microstructure. The microstructure of the alloys is more sensitive to Nb rather than Ta. The as-cast alloys exhibit needle-like α′ martensite at a lower Nb content of 3 wt.% and lamellar α′ martensite at an Nb content of 5 wt.%. Among the alloys, the Ti-3Nb-13Ta-2Zr alloy shows the highest compressive strength (2270 ± 10 MPa) and compressive strain (74.3% ± 0.4%). This superior performance is due to the combination of α+β dual-phase microstructure and stress-induced α" martensite. Besides, lattice distortion caused by Ta element also contributes to the compressive properties. Nb and Ta contents of the alloys strongly affect Young's modulus and tensile properties after rolling. The as-rolled Ti-3Nb-13Ta-2Zr alloy exhibits much lower modulus due to lower Nb content as well as more α" martensite and β phase with a good combination of low modulus and high strength among all the designed alloys. Atom probe tomography analysis reveals the element partitioning between the α and β phases in which Ta concentration is higher than Nb in the α phase. Also, the concentration of Ta is lower than that of Nb in the β phase, indicating that the β-stability of Nb is higher than that of Ta. This work proposes modern α+β dual-phase Ti- x Nb- y Ta-2Zr alloys as a new concept to design novel biomedical Ti alloys with high performance.