Mechanical twinning and omega transition by ⟨111⟩ {112} shear in a metastable β titanium alloy

Xing, Hui; Sun, Jie

doi:10.1063/1.2959183

Cited by 104 publications

(48 citation statements)

References 16 publications

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“…7), which can be described as a combination of x-phase with deformation twins caused by shearing [46]. Diffraction pattern presented as an inset displays diffusive lines between spots of (200) and (110) planes in [011] zone axis pattern.…”

Section: Resultsmentioning

confidence: 99%

Enhancement of mechanical properties of biocompatible Ti–45Nb alloy by hydrostatic extrusion

et al. 2014

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b-Type titanium alloys are promising materials for orthopaedic implants due to their relatively low Young's modulus and excellent biocompatibility. However, their strength is lower than those of a-or a ? b-type titanium alloys. Grain refinement by severe plastic deformation (SPD) techniques provides a unique opportunity to enhance mechanical properties to prolong the lifetime of orthopaedic implants without changing their chemical composition. In this study, b-type Ti-45Nb (wt%) biomedical alloy in the form of 30 mm rod was subjected to hydrostatic extrusion (HE) to refine the microstructure and improve its mechanical properties. HE processing was carried out at room temperature without intermediate annealing in a multi-step process, up to an accumulative true strain of 3.5. Significant microstructure refinement from a coarse-grained region to an ultrafine-grained one was observed by optical and transmission electron microscopy. Vickers hardness measurements (HV 0.2 ) demonstrated that the strength of the alloy increased from about 150 to 210 HV 0.2 . Nevertheless, the measurements of Young's modulus by nanoindentation showed no significant changes. This finding is substantiated by X-ray diffraction analyses which did not exhibit any phase transformation out of the bcc phase being present still before processing by HE. These results thus indicate that HE is a promising SPD method to obtain significant grain refinement and enhance strength of b-type Ti-45Nb alloy without changing its low Young's modulus, being one prerequisite for biomedical application.

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Section: Resultsmentioning

confidence: 99%

Enhancement of mechanical properties of biocompatible Ti–45Nb alloy by hydrostatic extrusion

et al. 2014

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“…The relationship between the MoE value and the phase stability diagram occurs because many of the beta stabilizing elements have similar 3d or 4s orbital electron configurations and comparatively low electronegativities and atomic radii. Research on stress-induced transformations is currently an active area of research due to its effect on mechanical response during deformation and its potential influence in engineering applications [24,112,[159][160][161][162][163]. A detailed review on this topic alone as provided by Kolli et al [33].…”

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confidence: 99%

A Review of Metastable Beta Titanium Alloys

Kolli

Devaraj

2018

Metals

430

175

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Abstract: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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“…9 (b) with widths ranging from 11.5 nm to 32.5 nm. Previous reports observed {112}〈111〉 mechanical twins in an Ti23Nb-0.7Ta-2Zr-1.2O (at.%) alloy [141,331]. However, this twinning system is absent in the present alloy as the increased levels of Nb and other β stabilisers result in an increased stacking fault energy [170].…”

Section: Resultscontrasting

confidence: 49%

“…Bertrand et al reported that different variants of α″ can be activated in the same β grains during deformation [140]. In addition, it was reported that a small amount of ω phase was detected in some alloys, but it cannot be confirmed by EBSD due to its nanometric size and coherence with the β phase [141]. the same area as in (a), (d) corresponding X-ray diffractogram of (c).…”

Section: Identification Of α″ Phasementioning

confidence: 71%

Mechanical and microstructural characterisation in the processing of biomedical metallic fine tubes

Yao-wu¹

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Fine tube stents are used for maintaining localised flow in stenotic blood vessels. Elasticity and plasticity for expansion, rigidity for resisting bending under force and strength to prevent unexpected failure, are required properties of the tubes from which these stents are formed. Biomedical metastable β titanium alloys have been developed as implant materials for a large number of biomedical applications due to a combination of favourable characteristics, e.g. good biocompatibility, excellent toughness and corrosion resistance. A metastable β alloy, Ti-25Nb-3Mo-3Zr-2Sn, has been developed without toxic alloying elements, which is a promising candidate material for stent applications. Metallic materials used for stents are commonly not biodegradable and implanted in the vessel permanently, which may provoke in-stent restenosis and stent thrombosis. In order to remove the implanted materials after service, biodegradable materials, absorbed by the body slowly, are also a field of research interest. Magnesium alloys have been used in studies for biomedical stent applications as a new biodegradable material. Magnesium stents can reopen the blocked blood vessels temporarily before degrading in physiological environments. In addition to the biodegradable characteristics, their mechanical properties are reasonable. The Mg-3Al-1Zn (AZ31) alloy is the subject of some research on the processing of biomedical magnesium alloys as it is a commonly available commercial alloy. Consequently, the Ti-25Nb-3Mo-3Zr-2Sn alloy and the AZ31 magnesium alloy have been used in this thesis to investigate the evolution of mechanical properties and microstructure in the processing of fine tubes.The deformation mechanisms during cold deformation of metastable β titanium alloys are mainly associated with martensitic phase transformations and mechanical twinning. It has been reported that stress-induced phase transformations and {112}〈111〉, {332}〈113〉 twinning modes may be activated under different stress states in metastable β titanium alloys. They can exhibit varying elasticity, Young's modulus and strain hardening behaviour. Because the martensitic start temperature is below room temperature for most metastable β titanium alloys, the α″ martensitic transformation can easily occur under a small amount of external stress. Mechanical twins were reported to hinder slip and dislocation motion thereby increasing the strain hardening rate. The development of β and α″ texture during processing is another critical influence on the mechanical properties of fine tubes. Therefore, studies on the martensitic transformation, mechanical twins and texture evolution is of significance in order to understand the processing of β titanium fine tubes.ii Magnesium alloys deform through the formation of a large amount of mechanical twins due to the relatively low critical stress to activate twinning in comparison with 〈 + 〉 slip. There are typically two primary mechanical twinning modes for magnesium alloys, {101 ̅ 2} extension twins and {101 ̅ 1} cont...

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Mechanical twinning and omega transition by ⟨111⟩ {112} shear in a metastable β titanium alloy

Cited by 104 publications

References 16 publications

Enhancement of mechanical properties of biocompatible Ti–45Nb alloy by hydrostatic extrusion

Enhancement of mechanical properties of biocompatible Ti–45Nb alloy by hydrostatic extrusion

A Review of Metastable Beta Titanium Alloys

Mechanical and microstructural characterisation in the processing of biomedical metallic fine tubes

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