Ti-V System Research Articles

Experimental study of density, molar volume and surface tension of the liquid Ti-V system measured in electromagnetic levitation

Systematical experimental data on density, molar volume and the surface tension, measured in electromagnetic levitation, has been summarized for the liquid Ti-V system. The optical dilatometry method as well as the oscillating drop technique have been employed to investigate the temperature- and compositional dependence. A linear decrease in density and surface tension with increasing temperature has been observed for all investigated compositions. Pure Vanadium shows hereby the highest density and surface tension while pure titanium shows the lowest density and surface tension respectively. Therefore, the density and surface tension decrease with increasing titanium content, however not linear. Since no excess quantities were available, simple models could be employed to cover the complete liquid Ti-V system. Experimental data as well as the corresponding linear fits are presented.

Surface tension of liquid Ti, V and their binary alloys measured by electromagnetic levitation

AbstractThe surface tension of the liquid Ti-V system is systematically measured using the oscillating drop technique during electromagnetic levitation. Temperature- and compositional dependence are both investigated. The entire compositional range is covered. A linear decrease with increasing temperature is found for the pure elements as well as for all investigated alloys. The surface tension generally increases with increasing V-content. The obtained data are in good agreement with the Butler model for the ideal solution. Additionally, the Butler model for the regular solution was evaluated in the context of the obtained surface tension data. In contrast to many other Ti-based alloys, the Butler model for the regular solution yields no additional benefit for Ti-V, since there is only a neglectable small deviation between the calculations for the ideal and regular solution. Segregation effects are modeled using the Butler equation for an ideal solution. The findings are discussed considering already existing trends for the mixing behavior of liquid Ti-alloys. The results strongly suggest, that the Ti-V system obeys in general the ideal solution law.

Sociocultural dimensions of early dual language learning

Titone and Tiv's Systems Theory of Bilingualism aims to “urge cognitive scientists and neuroscientists to better embrace sociolinguistic and sociocultural experiences as part of their theoretical and empirical purview”. No stronger case for such a framework can be found than in studies of developmental aspects of bilingualism. In fact, inclusion of sociocultural variation has been a common feature of many studies of dual language learning for some time, especially in studies of pre-school and early-school-age learners (see Genesee, 2019, for a review). Young dual language learners – neonates, infants and toddlers, exposed to more than one language – begin life as virtual tabula rasa and are capable of learning any language with facility. As a result, their language acquisition is necessarily tied to the sociocultural parameters of the learning environments they are exposed to. Moreover, as Titone and Tiv emphasize, the immediate and ultimate purpose of language learning is communication. Thus, young dual language learners must be attuned to and acquire the sociocultural constraints and norms for communicating effectively in more than one language. While sociocultural variation is important for understanding language acquisition even among monolingual children living in relatively homogeneous monocultural environments, sociocultural variation is inherent and, indeed, enhanced in the learning environments of children acquiring more than one language insofar as each language is intimately linked with different socio-cultural parameters. Sociocultural variation can be important for understanding bilingualism in yet another way. In studies of the neuro-cognitive consequences of bilingualism, it has been reported that there is a more pronounced association between dual language exposure and activation of certain brain areas among adolescent bilinguals from relatively low SES backgrounds than bilinguals from relatively high SES backgrounds (Brito & Noble, 2018). Inclusion of sociocultural variation in research on the effects of bilingualism can reveal a more nuanced view than emerges if such variation is not considered.

Sycophantic Culture and the Sustainability of Democracy in Nigeria

Since the return to democratic or civil rule in Nigeria in 1999, we have had the opportunity to take our cherished democracy through successful successive rebirths. Our democracy has been a major factor for the changes, development and growth which we share today. This democracy has also taught us to checkmate people placed in positions in our bid to fight poverty, ensure social cohesion, facilitate the development of our social services, deepen political participation and awareness, and above all, sustain the peace of one Nigeria. However, it is observed with great concern and urgency that there is this dangerous cancerous enigmatic culture which if not tackled, has the propensity to derail and crumble our gigantic efforts to build a better Nigerian democratic culture. This cancer is what I call “sycophantic culture” which is more dangerous than the coup makers. Hence, this paper argues that this sycophantic culture in our socio-economic and political lives is one of the biggest threats we face even as we shape our democracy. Using analytic, historical and expository stencils, the paper identifies the various shades and forms this culture has hindered the making of our national rebirth where merit strives, mediocrity is shunned, ethnic cleavages are integrated at a higher level and cheap religious sentiments down played. The paper concludes using Tiv system of moral justice which reveres the pride of truth telling as a strong panacea towards building an integrative Nigerian democratic variable culture.

Angular dependent interatomic potential for Ti-V system for molecular dynamics simulations

Abstract An interatomic potential for the Ti-V binary alloy focusing on evolution of defects, including ones arising as a result of the irradiation process, was constructed within the Lipnitskii-Saveliev approach, which accurately takes into account three-particle interactions and the sum of all multi-particle interactions of a higher order in the framework of the centrally symmetric approximation. In the new potential, Ti-V interactions were fitted to the DFT data on set of model structures with different coordination numbers, including ones with vacancies. The properties used for fitting are accurately reproduced by the present potentials for both pure elements and alloy systems. The potential was tested on the binding energies between Ti atoms and self-point defects in bcc V, elastic moduli, thermal expansion and melting point of some alloys, and diffusion. We obtained qualitative agreement for these properties with available theoretical and experimental data. Finally, we investigated evolution of excess vacancies in the V-4 at. \% Ti alloy at 700 K, which are typical conditions of vanadium-based alloys for fusion applications. We found that no vacancy loop is formed in the alloy in contrast to the pure V, which agrees with the experimental observations. The potential is expected to be especially suitable for irradiation simulations of vanadium based V-Ti alloys.

Mixing enthalpies of alloys with dynamical instability: bcc Ti-V system

Enthalpy of mixing is among the key materials parameters to determine phase stability and phase transformations in solid solutions. The possibility to predict it from first principles in the framework of the density functional theory is one of the corner stones of the modern materials modeling and the future data-driven materials design. Here we have considered body-centered cubic (bcc) Ti-V alloys, a system with high potential for aerospace, automotive biomedical and energy applications, which is known to exhibit the dynamical instability of the crystal lattice for Ti-rich alloys at low temperature. We have calculated the mixing enthalpies ΔH of bcc Ti-V alloys in the whole interval of concentration at high temperature using ab initio molecular dynamics (AIMD) simulations. A comparison with state-of-the-art static calculations at temperature 0 K shows drastic difference between the two methods: while AIMD predicts positive values of ΔH in the whole range of concentrations, the static zero-temperature simulations result in negative values of ΔH for Ti-rich alloys. We have measured the mixing enthalpy of bcc Ti-V alloys experimentally at 1073 K using an isoperibol high temperature Tian-Calvet calorimeter and found that the enthalpies are positive, in agreement with our finite temperature AIMD calculations. We attribute the failure of the standard static calculations of ΔH to lattice distortions associated with the dynamical instability of bcc Ti-V alloys at zero temperature and argue that the effect should be generally important in theoretical predictions of thermodynamic properties, especially for systems with dynamical instability.

The Effect of Oxygen on Phase Equilibria in the Ti-V System: Impacts on the AM Processing of Ti Alloys

Oxygen is always a constituent in “real” titanium alloys including titanium alloy powders used for powder-based additive manufacturing (AM). In addition, oxygen uptake during powder handling and printing is hard to control and, hence, it is important to understand and predict how oxygen is affecting the microstructure. Therefore, oxygen is included in the evaluation of the thermodynamic properties of the titanium-vanadium system employing the CALculation of PHAse Diagrams method and a complete model of the O-Ti-V system is presented. The β-transus temperature is calculated to increase with increasing oxygen content whereas the extension of the α-Ti phase field into the binary is calculated to decrease, which explains the low vanadium solubilities measured in some experimental works. In addition, the critical temperature of the metastable miscibility gap of the β-phase is calculated to increase to above room temperature when oxygen is added. The effects of oxygen additions on phase fractions, martensite and ω formation temperatures are discussed, along with the impacts these changes may have on AM of titanium alloys.

Molecular Dynamics Simulations of the Excess Vacancy Evolution in V and V-4Ti

Titanium additions suppress the radiation swelling in vanadium alloys, but the mechanism of the suppression is debatable. It is claimed that interactions of Ti atoms with vacancies in vanadium are crucial in the suppression. In this paper we study clustering of excess vacancies in pure V and V-4Ti by molecular dynamics simulations at 700 K based on our interatomic potentials constructed earlier for the Ti-V system. For pure V the process results in the formation of a Frank sessile dislocation while the clustering in V-4Ti ends with the formation of the Ti-vacancies complexes with a specific structure. This allows us to discuss a possible mechanism of the swelling reduction in V caused by Ti alloying.

Molecular dynamics simulation of nano-indentation on Ti-V multilayered thin films

We developed a second nearest-neighbor modified embedded-atom method potential for binary Ti-V system. The potential parameters were identified by fitting the lattice parameter, cohesive energy and elastic constants of CsCl-type TiV, and further validated by reproducing the fundamental physical and mechanical properties of Ti-V systems with other crystal structures. In addition, we also performed molecular dynamics simulations of nano-indentation processes of pure Ti film, pure V film, and two kinds of four-layer Ti-V films, V-Ti-V-Ti and Ti-V-Ti-V. We found that the indentation force-depth curve for the pure V film turns flat at an indentation depth of 2.8nm, where a prismatic loop was observed. Such prismatic loop is not found in the V/Ti/V/Ti multilayer because the thickness of each layer is insufficient for the formation of such prismatic loops, which accounts for the increase of stress in the multilayer.

Influence of aluminum and vanadium alloying elements on the resistivity of titanium

The experimental data on the resistivity of titanium-aluminum and titanium-vanadium alloys in the temperature ranges of 77–1700 and 77–350 K, respectively, at alloying component concentrations below 10 at % are generalized. At these concentrations, the isotherms of the dependences ρ(c) are linear in the temperature range of the α phase (77–500 K) and in the β phase. The numerical values of the concentration angular coefficients (dρ/dc)T = b were obtained for the Ti-Al and Ti-V systems at temperatures of 77 and 300 K and Ti-Al alloys in the β phase at T = 1400 K.

Thermodynamic study of Ti-V and Al-V systems using FactSage

Thermodynamic study of Ti-V and Al-V binary systems is presented in this paper. Investigations included thermodynamic determination of activities, coefficient of activities, partial and integral values Gibbs energies of mixing and excess energies at four different temperatures: 2000K, 2073K, 2200K and 2273K, as well as calculated phase diagrams for the investigated systems. The FactSage program was used for all thermodynamic calculations.

Structure and transformations of metastable phases. in Zr-Nb and Ti-V alloys

An experimental study is presented of the effect of an isothermal heat treatment ('aging') upon the structural properties of three metastable phases in Zr-Nb and Ti-V alloys, viz. α (hcp), β (bcc) and Ω, formed by quenching the alloys from 1273 K. Using neutron-diffraction experi- ments, the constitution of the aged alloys and the structural parameters of the resulting aged phases were determined. By combining lattice-parameter measurements with previously established correlations in the Zr-Nb and Ti-V systems, new information on the composition of the aged phases was ob- tained. For long aging times the α and β phases seem to be approaching equilibrium conditions, which opens up the possibility of using quenching-and-aging experiments to gain insight into the metastable phase diagram of these systems, which is not accurately known from experiments.

Metastable phases in the Ti-V system: Part I. Neutron diffraction study and assessment of structural properties

This article presents the results of a neutron diffraction study of a series of quenched Ti-V alloys and an assessment of the composition dependence of the structural properties in the Ti-V system. Upon quenching to room temperature and atmospheric pressure, three metastable phases occur, viz., the hcp (α′) phase formed by a martensitic transformation, the omega (Ω) phase formed by a displacive transformation involving the collapse of the (111) planes of the bcc structure, and the untransformed bcc (β) phase. The lattice parameters (LPs) of the α′, β, and Ω phases are determined as functions of the V content in the composition range 3 ≤ at. pct V ≤ 70. This information is combined with a detailed analysis of the available experimental data on the α′, β, and Ω phases in pure Ti and Ti-V alloys and the β phase of V. New estimates for the LPs of β and Ω Ti and expressions describing the composition dependence of the LPs are presented. Using the assessed values, various open questions are discussed, i.e., the composition range where the hexagonal to trigonal symmetry change is observed in the Ω phase, the applicability of an approximation involved in the plane collapse model for the β → Ω transformation, and the extent to which the so-called Jamieson correlation for interatomic distances in the Ω phase holds for Ti.

Metastable Structures, Bonding Properties and Phase Transitions in Alloys of the Zr-Nb and Ti-V Systems

Metastable Structures, Bonding Properties and Phase Transitions in Alloys of the Zr-Nb and Ti-V Systems

The effect of lattice relaxation and charge transfer on mixing energies and configurational interactions in alloys: cluster calculations for the dilute BCC Ti1-xVx and FCC Ni1-xAlx systems

We present self-consistent LMTO-ASA cluster calculations of the solution energy Q and the nearest- and next-nearest-neighbour configurational interactions, V1 and V2, for the dilute BCC Ti1-xVx and FCC Ni1-xAlx alloys. The lattice relaxation effects (LRE) are described with a proper choice of atomic volumes for the impurity and its neighbours, which are found employing the conventional phenomenological estimates for atomic displacements near an impurity. For the Ti-V system LRE are found to be important, while the charge transfer effects (CTE) are small. The results of our calculations for this system seem to indicate that the phenomenological estimates overestimate LRE contributions to Q and Vi by a factor of about two. We also present phenomenological estimates of LRE contributions to Q for impurities in 24 cubic host metals. For the Ni-Al system LRE are found to be small while CTE are significant, and taking them into account in the cluster calculations of Q and Vi seems to noticeably improve their accuracy as compared with single-site approaches.

Amorphization of the TiV system by mechanical alloying and mechanical grinding in a hydrogen and nitrogen atmosphere

A TiV system, which does not amorphize in an inert gas atmosphere, has been mechanically alloyed (MA) and mechanically ground (MG) using a planetary ball mill in a hydrogen and nitrogen atmosphere. The products were characterized by x-ray diffractometry, transmission electron microscopy, differential scanning calorimetry, and chemical analysis as a function of milling time and the gas pressure. Amorphization occurs by MA and MG in a hydrogen atmosphere and by MG in a nitrogen atmosphere. Amorphization by MA proceeds by the reaction between TiH2 and pure V in a hydrogen atmosphere, while it proceeds by MG by hydrogen and nitrogen absorption into the metastable β-TiV alloy and subsequent milling. The difference in the phase formation by MA and MG of the TiV system is discussed based on the gas absorption rate and the solubility of gases.

Phase selection in undercooled ti3sn melts

The solidification of undercooled Ti3Sn melts was investigated using electromagnetic levitation and electrohydrodynamic atomization experiments followed by extensive microstructural char- acterization. The study was motivated by several reports on the kinetic preference for the body- centered cubic (bcc) phase over more closely packed disordered and ordered structures during competitive crystallization from undercooled melts. At low undercoolings, Ti3Sn melts yield the equilibrium ordered hexagonal DO19 structure, which is retained without change upon cool- ing. Undercoolings between ~100 and ~300 K yield primary dendrites with hexagonal sym- metry but a final microstructure which is clearly martensitic in origin. Two previously unknown metastable forms of Ti3Sn were identified: an ordered base-centered orthorhombic derived from the α martensite and an ordered monoclinic phase related to the face-centered orthorhombic martensite observed in the Ti-V system. Both phases are believed to evolve from the solid state transformation of a high temperature β phase, but the dendritic structure clearly indicates the formation of a hexagonal phase different from DO19,i.e., α. The latter forms in preference to β, which has a larger driving force in at least part of the undercooling regime studied. It is proposed that the primary α transforms to β as a consequence of recalescence, which subse- quently transforms martensitically and orders to yield the observed metastable forms of Ti3Sn.

FIRST-PRINCIPLES APPROACH TO ALLOY PHASE STABILITY

Order-disorder phenomena and structural transformations in substitutional alloys are studied with a proper combination of quantum mechanics and statistical thermodynamics. The methodology is briefly presented and its predictive capabilities are illustrated for various alloys, including the bcc-based Ti-V, Ti-Fe and Cr-Fe systems, in terms of electronic structure, ground-state and short-range order diffuse scattering properties, and finally phase diagram results.

Particle coarsening behavior of α-β titanium alloys

A systematic study was undertaken to develop particle coarsening relationships in terms of time, temperature, and volume percents of phases and to determine the rate-controlling mechanisms for the coarsening of α-β Ti-Mn and Ti-V alloys. This investigation is confined to equiaxed-type α+ β microstructures. For a given alloy anc te nperature, the coarsening of particles refers to the growth of particles under essentially constant volume percents of the component phases. The coarsening exponents increased from 0 24 to 0.29 and from 0.28 to 0.32 for Ti-V and Ti-Mn systems, respectively, when the temperature was increased from 973 to 1073 K. In addition, it was found that the activation energy chances as the temperature is increased from 973 to 1108 K for the Ti-Mn system. Based on these results, it is suggested that the rate-controlling mechanism for particle coarsening changes from mixed (bulk + grain-boundary) diffusion control toward bulk diffusion control when the temperature is increased from 973 to 1108 K for the Ti-Mn system. Similarly, for the Ti-V system, it is suggested that the rate-controlling mechanism changes from grain-boundary diffusion control toward mixed diffusion control when the temperature is increased from 973 to 1073 K. These results clearly indicate that the rate-controlling mechanism depends on temperture as well as the diffusivities of the alloying elements.

The stable and metastable Ti-Nb phase diagrams

The phase transformations which occur in the Ti-Nb binary alloy system have been discussed in two recent papers. The phase relationships were investigated by varying alloy composition and thermal history. In this paper, these results are summarized in complete and thermodynamically consistent calculations of the stable and metastable phase diagrams. The calculations of the metastable equilibria are relevant to the Ti-V and Ti-Mo systems, as well as to several other titanium and zirconium-based transition metal alloy systems.