Development of high temperature Ti-Ta shape memory alloys

Miyazaki, S.; Kim, Hee Young; Buenconsejo, Pio John S.

doi:10.1051/esomat/200901003

Cited by 10 publications

(11 citation statements)

References 22 publications

(27 reference statements)

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“…In fact, due to the very weak

β

stabilizing effect, Zr is often referred to as being a neutral stabilizer . However, it has been experimentally found that high concentrations of Nb and Ta can convert Zr (and Hf) into a strong

β

stabilizer . Based on the picture of the electronic interactions in Ti and Ti alloys developed here, we tentatively attribute this behavior to the excess electrons from the Nb/Ta solutes that assist in further strengthening the Ti–Zr bonds in

β

Ti.…”

Section: Resultsmentioning

confidence: 65%

Importance of coordination number and bond length in titanium revealed by electronic structure investigations

Huang

Grabowski

McEniry

et al. 2015

Physica Status Solidi (b)

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We study the influence of coordination number and bond length on the phase stability and orbital occupation in Ti using density functional theory. In particular, Ti under a wide range of conditions (equilibrium state, hydrostatic pressure, anisotropic strain, and phase transformations) is systematically investigated allowing us to derive generic energetic and electronic trends. Our analysis of the correlations between electronic structure and the atomic geometry reveals that the most suitable descriptors of the system are an effective coordination number and an effective bond length. Utilizing these descriptors, we show that (i) the phase stability of Ti increases with coordination number, because of the increased number of interatomic bonds; (ii) the occupation number of the d (s and p) orbital decreases (increases) with increasing the bond length, because of the localized (delocalized) character of the d (p and s) orbital. These dependencies are particularly evident after applying a simple harmonic strain correction to the energy and an electron‐transfer correction within the ω phase. The physical picture derived from pure Ti is used to explain the phase stability and orbital occupation of Ti–Nb and Ti–Zr alloys, which reveals the underlying mechanisms for various experimental phenomena in Ti alloys.

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“…In fact, due to the very weak

β

stabilizing effect, Zr is often referred to as being a neutral stabilizer . However, it has been experimentally found that high concentrations of Nb and Ta can convert Zr (and Hf) into a strong

β

β

Ti.…”

Section: Resultsmentioning

confidence: 65%

Importance of coordination number and bond length in titanium revealed by electronic structure investigations

Huang

Grabowski

McEniry

et al. 2015

Physica Status Solidi (b)

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“…Ta-Ti alloys have been proposed as one of the best choices for biomedical applications based on their excellent biocompatibility in the human body environment, high strength, relatively low elastic moduli and enhanced corrosion resistance [1,2,3,4,5,6]. These alloys are also attractive for applications in advanced actuators since they exhibit shape memory behavior at relatively high temperatures due to a reversible martensitic transformation between the meta-stable bcc phase and the α" martensite phase [7,8,9,10,11,12,13]. Despite the potential applications of these alloys, important gaps exist in our knowledge of their binary phase diagram.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the tantalum-titanium phase diagram from ab-initio calculations

Barzilai¹,

Toher

Curtarolo

et al. 2016

Acta Materialia

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The thermodynamic properties of the Ta-Ti binary system below 900 0 C are not well known. In particular, the location and shape of the solvus between the phase separation region at low temperatures and the solid solution at high temperatures are not well defined. In this study, we present a thermodynamic description for this system based on ab-initio calculations. The formation enthalpies of bcc and hcp solid solutions are estimated using the special quasi-random structures methodology and their vibrational free energy calculated by the quasi-harmonic Debye model. The excess energies of the solid solutions are fitted to a sub-subregular model and used to define the phase diagram of the binary system. It is shown that the current empirical assessment of the energies of the pure elements leads to a phase diagram that strongly departs from the known experimental features at low temperatures. An ab-initio guided correction of these energies is necessary to obtain correctly the low temperature phase separation and the high temperature solid solution. The predicted solvus of the phase diagram is qualitatively different from those previously reported for the Ta-Ti system. It exhibits a miscibility gap between two distinct bcc phases, similar to those that exist in the closely related binary systems Ta-Zr, Ta-Hf, Cr-Ti, Mo-Ti, V-Ti, and Ti-W.

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“…At these temperatures, martensitic transformation is observed in Zr-based alloys (ZrCo, ZrCu, ZrCuCo, ZrCuNi, ZrCоNi, ZrRh), HfIr, ТiTa [42][43][44]. For example, in alloy Zr 2 CоNi, direct martensitic transformation is beginning at 600С during cooling, and reverse transformation under heating is finished at 900С; martensitic transition is characterized by wide temperature hysteresis.…”

Section: 2mentioning

confidence: 99%

Reversibility of the Martensitic Transformations and Shape-Memory Effects

Lobodyuk

2016

Usp. Fiz. Met.

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The results of the investigations of main peculiarities and reversibility of the martensitic transformations in different materials are considered and discussed. Unusual mechanical properties such as shape-memory effect, superelasticity, superplasticity, and other phenomena caused by these transitions are also analysed. The values of the recovering deformation are determined by the mechanism of the martensitic transformations and their reversibility. Reasons for their differences for the alloys with different characters of the martensitic transitions are also discussed.Розглядаються й обговорюються результати досліджень основних особ-ливостей та оборотности мартенситних перетворень в різних матерія-лах. Проводиться аналіза таких незвичайних механічних властивостей, як ефект пам'яти форми, надпружність, надпластичність, та інших явищ, спричинених такими переходами. Величини відновлюваної де-формації визначаються механізмом мартенситних перетворень та їх оборотністю. Також обговорюються причини їхніх різних значень у стопів із різними характерами мартенситних переходів.Рассматриваются и обсуждаются результаты исследований основных особенностей и обратимости мартенситных превращений в различных материалах. Проводится анализ таких необычных механических свойств, как эффект памяти формы, сверхупругость, сверхпластич-ность, и других явлений, вызванных такими переходами. Величины восстанавливаемой деформации определяются механизмом мартенсит-ных превращений и их обратимостью. Также обсуждаются причины их разных значений у сплавов с различными характерами мартенситных переходов.Keywords: alloy, phase, martensitic transformation, reversibility, morphology, defect structure. Успехи физ. мет. / Usp. Fiz. Met. 2016, т. 17, сс. 89-118 DOI: http://dx.doi.org/10.15407/ufm.17

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Development of high temperature Ti-Ta shape memory alloys

Cited by 10 publications

References 22 publications

Importance of coordination number and bond length in titanium revealed by electronic structure investigations

Importance of coordination number and bond length in titanium revealed by electronic structure investigations

Evaluation of the tantalum-titanium phase diagram from ab-initio calculations

Reversibility of the Martensitic Transformations and Shape-Memory Effects

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