Origin of {332} twinning in metastable β-Ti alloys

Tobe, Hirobumi; Kim, Hee-Young; Inamura, Tomonari; Hosoda, Hideki; Miyazaki, S.

doi:10.1016/j.actamat.2013.10.048

Cited by 162 publications

(66 citation statements)

References 59 publications

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“…The change of the mechanisms is due to Mo diffusion induced stability increase with coarsening iso particles. The suppression of {332}<113> twinning owing to the increased stability is well agreed with previous experimental results [11] and a recently proposed model [12]. After further coarsening of the iso phase and the presence of nano phase at 533K aging, deformation mechanisms were therefore largely suppressed, leading to brittleness in tensile test.…”

Section: Microstructure Investigations On Deformed Lta Samplessupporting

confidence: 78%

Strengthening Strategy for A Ductile Metastable B Titanium Alloy Using Low Temperature Aging

Sun¹,

Zhang²,

Brozek³

et al. 2016

Proceedings of the 13th World Conference on Titanium

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Low temperature aging treatments, at around isothermal transition temperature (T iso ), were performed on a ductile metastable Ti-12Mo alloy displaying a combination of TRIP (Transformation induced Plasticity) and TWIP (Twinning induced Plasticity) effects. The main objective is to improve the yield strength of the material while keeping the advantage of combined stress induced phase transformation and mechanical twinning, as observed in the solution treated samples. Based on a resistometric investigation dedicated to low temperature phases transformations, a set of short-time LTA treatments were performed. It is shown that, for aging temperature situated around T iso , tensile strength of Ti-12Mo can be largely enhanced without losing ductility. A superior combination of high strength (close to 1200MPa in true stress) and a stable plasticity of =0.4 (in true strain) was achieved with a significant strain hardening effect. IntroductionOver the last few decades, titanium alloys have been attractive materials for aerospace, biomedical and sporting goods industries and automotive applications due to their high strengthto-density ratio [1] good hardenability [2] and good corrosion resistance [3]. However, the poor average ductility of titanium alloys remains as a drawback when compared to steels or Co-Cr family of alloys. Promising mechanical properties have been recently investigated by our group and co-workers [4, 5, 6] on a metastable alloy, namely Ti-12Mo (wt. %). The experimental results showed that this alloy possessed a combination of high ductility (with an engineering elongation of about 53 56%) and high strain hardening rate thanks to a complex combination of stress induced transformation and intense mechanical twinning (combined TRIP/TWIP effects). It is known that the mechanical performances of metastable alloys can be optimized through various thermo-mechanical strategies [7] involving grain size reduction or secondary phase precipitation. Our approach of the latter strengthening strategy is actually based on a low temperatures thermal treatment [8] around the onset of isothermal omega precipitation. In metastable Ti alloys, the level of chemical instability of matrix is sensitive in the activation of stress induced phase transformations and mechanical twinning [4]. Therefore, the double objective of the research is to promote precipitation strengthening without excessive modification of β matrix chemical composition and with local coherent elastic stress between the particles and matrix, in order to maintain the combined TRIP and TWIP effects. Nucleation rate of omega phase mainly depends on temperature, whereas growth depends on time: therefore the mechanical properties of titanium alloys change drastically by the phase precipitation after long time aging. In that case, the large increase in yielding stress is detrimentally accompanied by a drastic reduction in ductility. Consequently, in this work, the low temperature aging (LTA) treatments have been performed for very short durations (from 60s to 600...

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Section: Microstructure Investigations On Deformed Lta Samplessupporting

confidence: 78%

Strengthening Strategy for A Ductile Metastable B Titanium Alloy Using Low Temperature Aging

Sun¹,

Zhang²,

Brozek³

et al. 2016

Proceedings of the 13th World Conference on Titanium

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“…According to a recently proposed mechanism, {112}<111> β twinning is the most common for stable bcc structures while {332}<113> β twinning is facilitated by lattice modulation of a destabilized bcc matrix [10].…”

Section: Introductionmentioning

confidence: 99%

Effect of Pd addition on the microstructure of Ti-30Nb alloy

et al. 2015

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The effect of Pd addition on deformation mechanisms, phase transitions and twinning has been extensively investigated in as-cast β-type Ti-30Nb (wt%) alloy using electron backscattered diffraction and transmission electron microscopy techniques. The addition of Pd resulted in refinement of the metastable ω phase. The {112}<111>-type twinning was found to strongly depend on the size of the ω particles. No β phase twins were observed in the binary alloy with larger ω particles. In the ternary alloy with much finer ω particles, {332}<113> and abundant {112}<111>-type twins were detected. On the contrary, the volume fraction of stress-induced α" martensite in the binary alloy was higher than that in the ternary one. Based on the analysis of phase diagrams and Gibbs free energy calculations, such complex phase transition and twinning phenomena have been explained in terms of relative phase stability between the ω particles and the β matrix.

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“…Another common deformation mechanism is mechanical twinning for β-Ti alloys which have low stacking fault energies [41]. In metastable β-Ti alloys, {112}〈111〉 and {332}〈113〉 twinning system have been reported [42,43].…”

Section: Microstructural Evolution Of β Titanium Alloys In the Procesmentioning

confidence: 99%

“…Several models of the movement of atoms required in {332}〈113〉 twinning have been reported [172,173], and it has been considered that instability of the metastable β-Ti phase allows complex movement of atoms and facilitates {332}〈113〉 twinning [174]. Tobe et al [41] studied {332}〈113〉 twinning and compared it with other twinning modes by taking account of the shear and shuffle mechanisms of the twinning modes, and concluded that lattice instability lowers the possibility of {112}〈111〉 twinning because additional shuffling to form the {112}〈111〉 twins is caused by the lattice modulation. Therefore, {332}〈113〉 twinning of the bcc structure was reported as the most likely twinning mode due to the required lower magnitude of shuffle in comparison with the other twinning modes.…”

Section: Martensitic Transformation and Heat Treatments On  Titaniummentioning

confidence: 99%

“…The martensitic α″ transformation can be triggered by external stresses for alloys which have a martensitic start temperature below room temperature as is the case for many of the metastable β titanium alloys [17,36,37]. Twinning is a common deformation mechanism for materials which have low stacking fault energies and bcc structures [41].…”

Section: Introductionmentioning

confidence: 99%

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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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Origin of {332} twinning in metastable β-Ti alloys

Cited by 162 publications

References 59 publications

Strengthening Strategy for A Ductile Metastable B Titanium Alloy Using Low Temperature Aging

Strengthening Strategy for A Ductile Metastable B Titanium Alloy Using Low Temperature Aging

Effect of Pd addition on the microstructure of Ti-30Nb alloy

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

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