Structure and properties of cast binary Ti-Mo alloys.

In this article, we provide a broad and extensive review of beta titanium alloys. Beta titanium alloys are an important class of alloys that have found use in demanding applications such as aircraft structures and engines, and orthopedic and orthodontic implants. Their high strength, good corrosion resistance, excellent biocompatibility, and ease of fabrication provide significant advantages compared to other high performance alloys. The body-centered cubic (bcc) β-phase is metastable at temperatures below the beta transus temperature, providing these alloys with a wide range of microstructures and mechanical properties through processing and heat treatment. One attribute important for biomedical applications is the ability to adjust the modulus of elasticity through alloying and altering phase volume fractions. Furthermore, since these alloys are metastable, they experience stress-induced transformations in response to deformation. The attributes of these alloys make them the subject of many recent studies. In addition, researchers are pursuing development of new metastable and near-beta Ti alloys for advanced applications. In this article, we review several important topics of these alloys including phase stability, development history, thermo-mechanical processing and heat treatment, and stress-induced transformations. In addition, we address recent developments in new alloys, phase stability, superelasticity, and additive manufacturing.

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A Review of Metastable Beta Titanium Alloys

https://hal.archives-ouvertes.fr/hal-00865174/document

Investigation of early stage deformation mechanisms in a metastable β titanium alloy showing combined twinning-induced plasticity and transformation-induced plasticity effects

https://www.nitinol.com/wp-content/uploads/2012/01/111.pdf

Formation and reversion of stress induced martensite in Ti-10V-2Fe-3Al

The effects of Ta content on the microstructures, dynamic Young’s modulus and tensile properties of the quenched Ti–Ta alloys were investigated for biomedical applications The microstructures were examined using a scanning electron microscopy (SEM) and an X-ray diffraction (XRD) analysis The results indicate that the microstructures of the quenched binary Ti–Ta alloys are sensitive to Ta content The Ti–Ta alloys exhibit lamellar HCP martensite (α′) structure at a Ta content below 20%, needle-like orthorhombic martensite (α″) structure at a Ta content between 30–50%, metastable β+α″ structure at a Ta content of 60%, and single metastable structure at a Ta content above 60% The dynamic Young’s modulus and tensile properties of the binary Ti–Ta alloys depend strongly on Ta content Ti–30% Ta and 70% Ta alloys have much lower modulus and a good combination of high strength and low modulus among all the studied Ti–Ta alloys They have the great potential to become new candidates for biomedical applications

Effects of Ta content on Young’s modulus and tensile properties of binary Ti–Ta alloys for biomedical applications

A detailed investigation has been made of the structure of alloys of the Ti-Mo system containing up to 10wt% Mo, water-quenched from theβ-phase region. With increase in molybdenum content, the martensite structure changes from hexagonal (α′) to orthorhombic (α″) at ∼4 wt% Mo, and at 10 wt% Mo, the structure is completely retained β. For alloy compositions <4 wt% Mo, there is a diffusional component in the transformation of the β-phase at the quench rates employed. There is a transition, with increase in molybdenum content, in morphology (from massive to acicular) and in substructure (from dislocations to twins). However, the transitions in crystallography, morphology and sub-structure are not directly related to one another except for an abrupt loss of dislocation substructure at theα′/α″ transition. The α toα″ crystallographic transition has the characteristics of a second order transformation, and evidence has been obtained of the existence of a spinodal within the metastable orthorhombic system. The orthorhombic martensites of Ti-6 and 8 wt% Mo decompose during quenching producing a fine modulated structure within the martensite plates, consistent with a proposed spinodal mode of decomposition.

Martensitic transformations in Ti-Mo alloys

The decomposition of Ti-Mo alloy martensites by nucleation and growth and spinodal mechanisms

An investigation is reported of martensite formation in certain Ti-Mo, Ti-V and Ti-Nb alloys and of the decomposition of martensite on ageing. A transition from hexagonal to orthorhombic martensite occurred with increase in solute content. On ageing the orthorhombic martensite structures, spinodal decomposition took place, accompanied by substantial strengthening. Reversion of α” to β can also occur in some alloys.

R. Davis

Papers

Martensitic transformations in Ti-Mo alloys

The decomposition of Ti-Mo alloy martensites by nucleation and growth and spinodal mechanisms

Martensite Formation and Decomposition in Alloys of Titanium Containing β-Stabilizing Elements