Strengthening mechanism and corrosion resistance of beta-type Ti-Nb-Zr-Mn alloys.

Design of low modulus β-type titanium alloys by tuning shear modulus C44

Self-healing of Al2O3 containing Ti microparticles

β-Type Ti-Nb-based alloys exhibit satisfactory biocompatibility and low Young’s modulus for biomedical applications. The microstructure and mechanical properties of a series of Ti-(14, 16, 18, 20, 22, 24)Nb-2Fe alloys fabricated by arc melting were investigated by XRD, optical microscopy, and tensile tests. Both ω and α″ phases existed in the Ti-14Nb-2Fe alloy, while just a single β phase existed in the other alloys. Twinning is an important deformation mechanism that causes work hardening and twinning-induced plasticity. It was found in the Ti-(14, 16, 18, 20)Nb-2Fe alloys and not in the Ti-22Nb-2Fe alloy. The Ti-14Nb-2Fe alloy exhibited the highest tensile strength and the highest Young’s modulus owing to the existence of the ω phase. The tensile strength decreased gradually from 830 MPa (highest) for the Ti-14Nb-2Fe alloy to 540 MPa (lowest) for the Ti-24Nb-2Fe alloy with an increase in the Nb content. The Young’s modulus decreased from 90 GPa for the Ti-14Nb-2Fe alloy to 63 GPa for the Ti-22Nb-2Fe alloy and then increased to 71 GPa for the Ti-24Nb-2Fe alloy. Elongation shows the same trend as the Young’s modulus. The Ti-22Nb-2Fe alloy, with a low Young’s modulus of 63 GPa, tensile strength of 570 MPa, and 15% elongation, was found suitable for biomedical applications. The Ti-20Nb-2Fe alloy also exhibits a high tensile strength, a Young’s modulus ratio of 9.24 × 10−3, and 18% elongation and is thus considered another valuable Ti alloy for biomedical applications.

Effect of Nb Content on Microstructures and Mechanical Properties of Ti-xNb-2Fe Alloys

Reduction of the manufacturing cost of titanium and the development of new alloys are crucial to effectively harvest the benefits derived by the use of titanium in industrial applications. Therefore, we considered the creation of new Ti-2X-2Z alloys via the combined lean additions of isomorphous (i.e. Nb) and eutectoid (i.e. Cu, Mn, and Fe) beta stabilisers, and systematically analysed their effect on the manufacturability and mechanical response of titanium produced via powder metallurgy. It is found that the addition of the alloying elements reduces the compressibility of the powder blend but enhances the densification. The microstructure of titanium is transformed into a Widmanstätten structure composed of α grain boundaries and α+β lamellae where the stronger the beta stabilisers the more refined the microstructural features, and no intermetallic phases are precipitated despite the use of eutectoid stabilisers. Consequently, the combined addition of isomorphous and eutectoid beta stabilisers has a significant effect on the mechanical response with the material becoming stronger, harder and less tough with the increment of the potency of the added beta stabilisers; however, the Ti-2X-2Z alloys share similar strengthening mechanisms. A more accurate theoretical equation for developing titanium alloys through the molybdenum equivalent parameter should be developed. 

Effect of combined lean additions of isomorphous and eutectoid beta stabilisers on the properties of titanium

Microstructures and mechanical properties of Mn modified, Ti-Nb-based alloys

The effects of step-quenching on the microstructure and mechanical properties of a binary Ti–10Mo (wt%) alloy were investigated by transmission electron microscopy. The step-quenching treatment, consisting of solution treatment in the β phase field at 850 °C followed by step-quenching to the α/β two-phase region at 650 °C and holding for 0.5 h, was employed before water-quenching the alloy to room temperature. Direct quenching from 850 °C to room temperature with or without an aging step at 650 °C was also conducted for comparison. Microstructural observation revealed that step-quenching favored the formation of α precipitates thinner than 20 nm in the absence of α″ or ω heterogeneous nucleation agents and effectively moderated the subsequent α″ martensitic transformation by increasing the stability of the β phase. Step-quenching generated a multiphase microstructure comprising α″, β, ω, and α phases by balancing the competitive martensitic α″ and diffusional α transformations. Only α″ martensite was formed in the β matrix after direct water-quenching; the mixture of α″ + β phases was transformed to a lamellar α + β microstructure with 5 min aging. The kinetics of α precipitation was calculated to illustrate the temperature dependence of α precipitation behavior during step-quenching. Direct water-quenching produced a tensile strength of 688 MPa and 36% ductility. After aging, the tensile strength was increased to 837–867 MPa, while the ductility was decreased to 5%. By step-quenching, the high tensile strength of 790 MPa and ductility of 23% were achieved.

H. Jiang

Papers

Microstructures and mechanical properties of Mn modified, Ti-Nb-based alloys

Effects of step-quenching on the α ″ martensitic transformation, α precipitation, and mechanical properties of multiphase Ti–10Mo alloy

Influence of cooling path after rolling on sulfide stress cracking behavior for casing steel