Relative strength of phase stabilizers in titanium alloys

Tegner, Bengt E.; Zhu, Linggang; Ackland, Graeme J.

doi:10.1103/physrevb.85.214106

Cited by 31 publications

(19 citation statements)

References 30 publications

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“…Fitting to these properties ensures that hcp is the most stable phase at T=0 and sets the correct energy scale. It should be noted that according to the ab initio calculations the Ti bcc phase is mechanically unstable at T=0 (C 11 < C 12 ) [5,7,30,31]. Therefore, reproducing the target values at T=0 for this phase does not ensure the correct description of this phase at high temperatures (including its mechanical stability).…”

Section: Potential Development Proceduresmentioning

confidence: 99%

“…As was mentioned above, the ratio of the elastic constants, C 11 /C 12 for the Ti bcc phase is less than 1 at T=0 [5,7,30,31]. Therefore, even excellent reproduction of the ab initio data on the bcc lattice parameter and relative (to hcp) formation energy at T=0 does not really provide any reliability of a semi-empirical potential at high temperature.…”

Section: Stability Of the Bcc Phasementioning

confidence: 99%

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Development of an interatomic potential for the simulation of defects, plasticity, and phase transformations in titanium

Mendelev

Underwood

Ackland

2016

The Journal of Chemical Physics

142

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New interatomic potentials describing defects, plasticity, and high temperature phase transitions for Ti are presented. Fitting the martensitic hcp-bcc phase transformation temperature requires an efficient and accurate method to determine it. We apply a molecular dynamics method based on determination of the melting temperature of competing solid phases, and Gibbs-Helmholtz integration, and a lattice-switch Monte Carlo method: these agree on the hcp-bcc transformation temperatures to within 2 K. We were able to develop embedded atom potentials which give a good fit to either low or high temperature data, but not both. The first developed potential (Ti1) reproduces the hcp-bcc transformation and melting temperatures and is suitable for the simulation of phase transitions and bcc Ti. Two other potentials (Ti2 and Ti3) correctly describe defect properties and can be used to simulate plasticity or radiation damage in hcp Ti. The fact that a single embedded atom method potential cannot describe both low and high temperature phases may be attributed to neglect of electronic degrees of freedom, notably bcc has a much higher electronic entropy. A temperature-dependent potential obtained from the combination of potentials Ti1 and Ti2 may be used to simulate Ti properties at any temperature.

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Section: Potential Development Proceduresmentioning

confidence: 99%

Section: Stability Of the Bcc Phasementioning

confidence: 99%

Development of an interatomic potential for the simulation of defects, plasticity, and phase transformations in titanium

Mendelev

Underwood

Ackland

2016

The Journal of Chemical Physics

142

View full text Add to dashboard Cite

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“…Zener et al first proposed that shear modulus C', which represents the resistance to {110}<11 _ 0> shear and is controlled by e/a ratio, can be employed to evaluate the stability of bcc structure (Zener, 1947). Early studies showed that the Young's modulus of β-type Ti polycrystals decreases with decreasing C', accompanied by a decrease in β-phase stability (Guo et al, 2014;Hu et al, 2008;Obbard et al, 2011;Tegner et al, 2012;Zener, 1947). Therefore, C' was once considered as the only parameter evaluating the β-phase (bcc) stability, especially in binary β-type Ti alloys.…”

Section: Resultsmentioning

confidence: 99%

“…As far as β-type Ti alloys with bcc structure, shear modulus C', which is equivalent to (C 11 -C 12 )/2 and represents the stability of β phase with respect to {110}<11 _ 0> shear, was once considered as the most important factor controlling the Young's modulus of polycrystal (Zener, 1947), because the Young's modulus decreases with decreasing the β-phase stability (Abdel-Hady et al, 2006;Guo et al, 2014). Thus, previous studies were mainly focused on clarifying the key role of shear modulus C' on the Young's moduli of polycrystalline β-phase Ti alloys (Hu et al, 2008;Obbard et al, 2011;Tegner et al, 2012). Actually, from the viewpoint of crystallography, in addition to C', C 44 should also be considered as a key parameter for evaluating β-phase stability, since C 44 represents resistance to {001}<100> shear (Otsuka et al, 2005), being similar to C' corresponding to {110}<11 _ 0> shear.…”

Section: Introductionmentioning

confidence: 99%

Origin of ultralow Young׳s modulus in a metastable β-type Ti–33Nb–4Sn alloy

Hou

Guo

Qiao

et al. 2016

Journal of the Mechanical Behavior of Biomedical Materials

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Although there is difficulty in growing a Ti-33Nb-4Sn single crystal due to its ultralow β-phase stability, the single-crystal elastic constants of metastable β-type Ti-33Nb-4Sn (wt%) alloy were extracted successfully from its polycrystal by in-situ synchrotron X-ray diffraction technique, to clarify the origin of the ultralow Young's modulus in its polycrystal. It is indicated that compared to binary TiCr, TiV and TiNb alloys, the Ti-33Nb-4Sn alloy possesses slightly lower β-phase stability with respect to {110}<110>(-)shear (i.e., C׳) but much lower β-phase stability regarding to {001}〈100〉 shear (i.e., C44). An analysis by the Hill approximation suggests that the ultralow isotropic polycrystalline Young׳s modulus (EH) of Ti-33Nb-4Sn alloy originates from the extremely low shear modulus C44 as well as the relatively low C׳. This indicates that in addition to C׳, C44 has a significant contribution to the Young's modulus of polycrystal, which challenges a conventional understanding that the Young's modulus of β-type Ti alloys is predominantly determined by C׳.

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“…To remove possible surface layers, moulded bars were straight-turned to a final diameter of 12mm and ground (ASTM P800) to produce a smooth finished surface for the oxidation tests. Nb and V are strong stabilizers of the cubic β-titanium phase [6,22], therefore, the amount of niobium and vanadium had to be limited to 2% to exclude the formation of a two-phase alloy. For sample production, the bars were sectioned into slices of 10mm length by low-speed disc cutting and again ground with P800 grinding paper.…”

Section: Sample Preparationmentioning

confidence: 99%