Ni Ta System Research Articles

Effect of tantalum ion implantation on deformation behavior and fracture of TiNi SMA. Part I. quasi-static tension

The effect of high dose implantation of Ta+ ions (Dion = 5′1016 cm−2) into samples from a TiNi shape memory alloy (SMA) on patterns of deformation and fracture mechanisms under quasi-static uniaxial tensile loads was studied. Using X-ray diffractometry, transmission electron microscopy, and scanning electron microscopy, it was shown that ion implantation resulted in amorphization of the surface layer with a thickness of ∼100 nm due to the formation of a chemical composition of approximately Ti36Ni41Ta23 (at.%), thermodynamically corresponding to the highest glass forming ability in the Ti–Ni–Ta system. In the implanted surface layer, both the microstructure and crystal structure defects subsystem were modified at a depth of ∼5 mm. Using the digital image correlation (DIC) method, the dynamics of changes in the integral and local (εyy longitudinal, εxy shear and εxx transverse) strain components were investigated in the tensile tests of both as-received and implanted TiNi SMA samples. On the basis of the obtained results, both integral and local stress–strain diagrams were plotted. In all studied cases, the main contribution to strain accumulation was made by the εyy and εxx strains, which differed significantly for the as-received and implanted TiNi SMA samples. It was concluded that the positive effect of ion implantation was manifested in loading ranges close to the martensitic yield stress (at strain range of 1–6%), despite a noticeable decrease in the ultimate tensile strength and plasticity of the implanted TiNi samples.

High-throughput measurements of interdiffusivities in fcc Co–Ni–Ta alloys at 1373K and 1473K

The composition-dependent interdiffusivities in the fcc Co–Ni–Ta alloys at 1373 K and 1473 K were deduced by using our newly developed numerical inverse scheme that combines two-dimensional (2D) simulations with diffusion triple experiments. This approach largely reduced the experimental efforts by analyzing only one single-phase diffusion triple at each temperature yet covering a much wider composition range than diffusion couples. The reliability of the high-throughput results was firstly verified by reproducing the experimental 2D composition profiles in each triple. In order to further validate the deduced interdiffusivities, several traditional one-dimensional (1D) diffusion couples were also devised, and the widely recognized Sauer-Freise method and Whittle-Green method were then employed to calculate the interdiffusivities for the binaries and at the intersection points within the ternary composition range, respectively. The interdiffusivities extracted from the inverse scheme agree well with those from the traditional approaches, which strongly proves the applicability of the present new scheme. Besides, the constructed main interdiffusivity planes at 1373 K and 1473 K provide an overview of the diffusion behavior in the fcc Co–Ni–Ta system and promote further kinetic studies.

Development of a Diffusion Mobility Database for Co-Based Superalloys

To facilitate the development of high-temperature Co-based γ-γ′ superalloys, a Co-Ni based diffusion mobility database is developed for the eight component FCC (Face Centered Cubic) system of Co-Al-W-Ni-Cr-Ti-Ta-Re. A CALPHAD approach is used to represent the temperature and composition dependency of the multicomponent system. The mobility descriptions were based on previous assessment work for the Ni-based superalloys, published experimental and computational data, and established diffusion correlations. The initial mobility descriptions were then refined using additional diffusion couple experimental data, particularly for the Co-Cr, Co-Ta, and Ni-Ta systems. After re-optimizing the descriptions with the new experimental data, the mobility descriptions were validated using a collection of published diffusion couple composition profiles, which were not included in the initial assessment process.

Combinatorial Investigation of the Ni–Ta System via Correlated High‐Speed Nanoindentation and EDX Mapping (Small Methods 2/2022)

Inside Front Cover In article number 2101084, Wheeler and co-workers demonstrate a direct method for correlating compositional and mechanical datasets from high-speed nanoindentation and EDX maps. They demonstrate this method combinatorially on a Ni–Ta diffusion couple, which includes five intermetallic phases with varying properties. This method yields paired compositional and mechanical data from any microstructural cross-section, independent of spatial distribution and morphology.

Combinatorial Investigation of the Ni-Ta System via Correlated High-Speed Nanoindentation and EDX Mapping.

Correlated high-speed nanoindentation and energy-dispersive spectroscopy are applied in a combinatorial investigation of the Ni-Ta system. All seven phases in the system are clearly resolved in the resulting maps, and the mechanical properties and composition ranges for each phase are determined. Good agreement with ab initio calculations is generally observed with some exceptions, most notably NiTa2 . This is achieved using a simple correlation method utilizing directly overlaid data matrices to allow compositional labeling of mechanical data. This allows easy data segmentation without requiring complicated statistical deconvolution methods. Without this correlative method, phase deconvolution of the Ni-Ta system would be challenging due to several phases possessing adjacent compositions and mechanical properties. This demonstrates the potential of this new correlative approach for future investigations, particularly those involving complex microstructures and/or compositional variation.

Thermodynamic description of the Co–Ni–Ta system

The temperatures of two invariant reactions λ3 → fcc(Co) + Co3Ta and λ3 → Co3Ta + λ2 in the Co–Ta system were identified to be 1320 and 1303 K, respectively, by Differential thermal analysis (DTA). The Co–Ta, Ni–Ta and Co–Ni–Ta systems were optimized using the CALculation of PHAse Diagram (CALPHAD) method based on the present experimental results and literature data. Three Laves phases λ1, λ2 and λ3 were described using a two-sublattice model (Co,Ni,Ta)0.6667(Co,Ni,Ta)0.3333, and compound (Co,Ni)Ta was modeled as (Co,Ni,Ta)1Ta4(Co,Ni,Ta)2(Co,Ni,Ta)6 by a four-sublattice model. A set of reliable and self-consistent thermodynamic parameters was obtained, which can be used for a variety of thermodynamic calculations and database establishment of the Co–Ni-based superalloys.

Thermodynamic optimization of the Ni–Ta system supported by the key experiments

The Ni–Ta system was experimentally determined and thermodynamically optimized in the present work. In experimental work, 12 as-cast and 12 annealed alloys were measured using scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX) and powder X-ray diffraction (XRD) techniques, and 5 crucial annealed alloys were determined using differential scanning calorimetry (DSC) method. It was found that Ni8Ta did not exist in both as-cast and annealed samples, and then two invariant reactions liq. → fcc(Ni) + Ni3Ta and liq. → Ni2Ta + μ-NiTa were modified. In the thermodynamic optimization, the solution phases liquid, fcc(Ni) and bcc(Ta) were treated with a substitutional solution model, three compounds Ni3Ta, Ni2Ta and NiTa2 were described using a two-sublattice model, and the compound μ-NiTa was modeled as (Ni,Ta)1Ta4(Ni,Ta)2(Ni,Ta)6 using a four-sublattice model. A set of self-consistent thermodynamic parameters of the Ni–Ta system was obtained.

Composition formulas of Ni-(Nb, Ta) bulk metallic glasses

It is known that bulk metallic glass compositions can be well interpreted by cluster formulas for stable liquids [cluster](glue atom)1 or 3, where the clusters are derived from relevant devitrification phases. In the present work, the glass forming composition formulas in Ni-Nb and Ni-Ta systems are fully examined. The procedures include choosing the appropriate eutectic crystalline phases, selecting the principal clusters via the criteria such as spherical periodicity and cluster isolation degree, and determining the glue atoms. After strictly following these procedures, the best glass forming compositions Ni62Nb38 in Ni-Nb system and the range 59–62 at.% Ni in Ni-Ta system are explained by formulas [Ni-Nb4Ni8]Nb2Ni and [M-Ni6Ta6]Ni3 (M is a random mixture of Ni and Ta) respectively.

Separating the strengthening phase in nickel–cobalt alloys doped with tantalum

The hardness values of monophasic (fcc solid solution) and biphasic (fcc solid solution and separated phase) nickel–cobalt alloys doped with tantalum are determined using the Vickers method. Based on the resulting data, a composition–structure–hardness diagram is devised for the Co–Ni–Ta system.

Isothermal section at 1100 °C of the Fe–Ni–Ta system

The isothermal section of the Fe–Ni–Ta system at 1100 °C was constructed using 6 diffusion couples and 10 alloys, the compositions of which were selected on the basis of the experimental results of the (Fe–Ni alloy)/Ta diffusion couples. The samples were examined by means of optical microscopy, scanning electron microscopy, and electron probe microanalysis. Experimental results showed no existence of ternary compounds at 1100 °C. The following five three-phase equilibria were observed: (1) (Ta) + Ta 2Ni + Ta(Fe, Ni), (2) Fe 2Ta + Ta (Fe, Ni) + TaNi 2, (3) Fe 2Ta + TaNi 2 + TaNi 3, (4) Fe 2Ta + TaNi 3 + (Fe, Ni), (5) TaNi 3 + TaNi 8 + (Fe, Ni). The compounds FeTa and NiTa formed continuous solid solution. The solubility of Fe in TaNi 2 and TaNi 3 was determined to be 18 and 7.8 at.%, respectively, while the solubility of Ni in Fe 2Ta was estimated to be 40 at.%.

Solution-based thermodynamic modeling of the Ni–Ta and Ni–Mo–Ta systems using first-principle calculations

Solution-based thermodynamic descriptions of the Ni–Ta and Ni–Mo–Ta systems are developed with supporting first-principles calculations and reported experimental data for parameter evaluation. For the Ni–Ta system, the liquid, bcc and fcc phases are described with a random solution model, D0 22–Ni 3Ta is treated as a stoichiometric compound, and the remaining compounds are modeled as solid solutions on multiple sublattices. The resulting model for the Ni–Ta system is integrated with reported treatments of the Ni–Mo and Mo–Ta systems, and a thermodynamic model for the ternary Ni–Mo–Ta system is developed. The zero-Kelvin enthalpies of formation for the intermetallic compounds in the Ni–Mo–Ta system and the enthalpies of mixing for the bcc and fcc special quasirandom structures (SQS) in the binary Ni–Ta system are computed using the Vienna Ab-initio Simulation Package (VASP). Phase equilibria modeling results for the ternary Ni–Mo–Ta system are summarily presented in the form of isothermal sections and liquidus projections, with appropriate comparisons with available experimental data.

Phase Equilibria of the Co—Ni—Ta System at 1100 °C.

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Phase equilibria of the Co–Ni–Ta system at 1100 °C

The phase equilibria of the Co–Ni–Ta system at 1100 °C are investigated using diffusion couples and five equilibrated alloys. The samples are examined by means of optical microscopy, scanning electron microscopy, and electron probe microanalysis. The experimental results show no existence of ternary compounds at 1100 °C. The following 4 three-phase equilibria are observed: (1) Ta(Co, Ni) + β-TaCo 2 + TaNi 3; (2) Ta(Co, Ni) + TaNi 2 + TaNi 3; (3) β-TaCo 2 + TaNi 3 + (Co, Ni); and (4) TaNi 3 + TaNi 8 + (Co, Ni). The compounds Ta 2Co and Ta 2Ni form continuous solid solutions. It is also the case for TaCo and TaNi. The solubilities of Co in TaNi 3, and Ni in β-TaCo 2 were determined to be up to 70 at.% Co and 30 at.% Ni, respectively.

Amorphization in Ni-Ti-Ta system through mechanical alloying

In recent years, advances have been made in synthesizing amorphous alloys with superior properties via solid-state reactions as opposed to traditional rapid solidification techniques [1, 2] because of improved properties of the alloys produced by the former techniques. Of the many solid-state reaction techniques, mechanical alloying (MA) has proven to be a simple yet very effective technique for producing amorphous alloys. Ever since the amorphization in mechanically alloyed Ni60Nb40 powder mixture was achieved by Koch [3], the technique has been widely applied for various binary systems. However, amorphization in ternary alloys have hardly been studied [4–7]. The reason being, a lack of proper understanding of the process and variation of the products with subtle changes in the process parameters. Mechanical alloying of both Ni-Ti and Ni-Ta systems has been studied extensively [2, 8–11], but no attempt has been made on mechanical alloying of the ternary Ni-Ti-Ta system. Ta, added as a ternary element in the NiTi-alloys has been proven to impart radiopassity, thermal stability, etc. [12, 13]. Hence in this research, an attempt has been made to study the amorphous phase formation in the (Ni51Ti49)1−xTax system in the range of 0–20 at.% Ta through mechanical alloying. Pure powders (99.9%) of Ni, Ti and Ta with particle sizes less than 45 μm (-320 mesh) were mixed under inert argon atmosphere according to the formula (Ni51Ti49)1−xTax (x = 0, 2, 4, 10, 15, 20). All powder mixtures were subjected to high-energy ball milling (HEBM) in a SPEX 8000 mill. A ball to powder ratio (BPR) of 10:1 was maintained with stainless steel balls of two diameters (0.5 in. and 0.25 in.) as grinding medium. All powder mixtures were initially milled for 0.5 hr and then powders with Ta at 4 and 20 at.% were subjected to 24 hrs of milling to study the process of amorphization in the system. Microstructural analysis to assess the overall physical particle size variation and interlayer thickness of the alloyed particles with milling time was performed using a scanning electron microscope (SEM). Phase transformation during the process of amorphization was performed using a Bruker Axis transmission powder diffractometer with Mo-Kα radiation (0.71073A). In order to conduct both microstructure and phase analyses, a small amount of powdered mixture was

Glass-forming ability determined from inter-atomic potentials for some miscible/immiscible binary metal systems

The present study attempts to clarify one of the important issues in the field of metallic glasses (or amorphous alloys), i.e., to predict the glass-forming ability/range (GFA/GFR) of the binary metal systems. Firstly, a brief summary of the experimental observations indicates that in the miscible/immiscible systems, amorphous alloys can be formed in a broad composition range extending from central portion to nearby the edges of the two terminal solid solutions. Consequently, to predict RFA/GFR of a system becomes an issue of determining the critical solid solubility of the system, beyond which a solid solution would collapse into an energetically favored amorphous state. Secondly, the n-body potentials are derived by routine methods for the miscible Ni-Ta, Ni-Mo, and Ni-Ti systems, whereas for the immiscible Ag-Co and Cu-W systems having no any equilibrium alloy, the cross potentials are fitted to some physical properties acquired by first principles calculation for a few possible nonequilibrium alloys. Thirdly, applying the proven realistic potentials, molecular dynamics simulations with solid solution models reveal that the physical origin of crystal-to-amorphous transition is the lattice collapsing while solute atoms exceeding the critical solid solubility and that the GFRs of the systems are within the composition ranges bounded by the two determined critical solid solubilities. It turns out that the predictions are in good agreement with the experimental observations.

Solubility criterion for sequential disordering in metal-metal multilayers upon solid-state reaction

An n-body Ni-Ti potential is derived and applied in a molecular dynamics simulation to study the maximum supersaturated solubility of the terminal solid solutions and solid-state reaction in a Ni/Ti bilayer. It reveals that during interfacial reaction of the Ni/Ti bilayer the Ti lattice reaches its maximum solubility by dissolving Ni earlier than Ni does through dissolution of Ti, which results in a sequential disordering of first Ti and then Ni, although Ti has a higher melting point than Ni. In the Ni-Zr, Ni-Mo and Ni-Ta systems, however, the Ni lattice collapses more rapidly because it reaches a maximum solubility earlier than its partners, which have higher melting points than Ni. A solubility criterion is thus relevant for all the above cases; the lower the maximum solid solubility the less stable is the lattice of the metal upon solid-state reaction.

Interfacial reaction, amorphization transition, and associated elastic instability studied by molecular dynamics simulations in the Ni-Ta system

By means of constant-pressure molecular dynamics simulation, the crystal-to-amorphous transition in the Ni-Ta system is investigated in detail. An n-body potential is first developed for the system in the framework of an embedded-atom method and is then applied to simulate the crystal-to-amorphous transition at the interfaces in a Ni-Ta sandwich model. It is found that the amorphous layers initiate to grow at the interfacial areas and extend to Ni and Ta lattices by crossing-interface atomic migration. Simulation is also performed on the models consisting of Ni- and Ta-based solid solutions and it reveals that the crystal-to-amorphous transitions take place at two respective critical solute concentrations, from which the composition range favoring metallic glass formation is thus determined. In addition to a structural change, a dramatic softening in shear elastic moduli is in association with the glass transition, which is therefore considered to be triggered by a mechanical instability. A brief discussion is also presented to compare the simulation results with those proposed criteria for solid-state amorphization.

Oxidation processes of alloys of the Ni—Ta system. II. Oxidation of the intermetallic compound NiTa

The oxidation kinetics of the intermetallic compound NiTa was studied by the continuous thermogravimetry in air at temperatures ranging from 600 to 1000°C. The scale formed was subjected to X-ray and metallographic sectioning phase analysis. Oxidation of NiTa was shown to occur because of the preferential diffusion of oxygen toward the scale-alloy interface. The kinetics is described as a parabolic function of time. The isotherms indicate that the parabolic oxidation rate constant Kp periodically decreases for t≤800°C but increases and periodically decreases for t>800°C. The temperature dependence of Kp is exponential. At t∼850°C the oxidation rate decreases, indicating a change in the oxidation mechanism. The scale formed on NiTa was found to contain the oxides NiO, NiO·Ta2O5(NiTa2O6), and Ta2O5, as well as Ni. The solid solutions Ni(Ta) and Ni3Ta were detected in the sublayer of scale adjacent to the alloy. At high temperatures those phases are distributed among the layers: NiO+NiTa2O6+Ta2O5 in the first, NiTa2O6+Ta2O5 in the second, Ni+Ta2O5 in the third, and Ta2O5+Ni(Ta)+Ni3Ta in the fourth. By analogy with the oxidation of unalloyed tantalum the explanation for the experimental results is that at a p→n phase transition. accompanied by the formation of oxygen vacancies and tantalum interstitials, occurs in the lattice at t∼850°C.

Formation of nonequilibrium solid phases by ion irradiation in the Ni-Ta system and their thermodynamic and growth-kinetics interpretations.

In the Ni-Ta system, several amorphous alloys were synthesized by room-temperature 200-keV xenon-ion irradiation of multilayered films with various compositions. The metallic-glass-forming range was determined experimentally to extend from 25 to 75 at. % Ni. In addition, a hcp metastable crystalline (MC) phase was observed in the Ni-rich ${\mathrm{Ni}}_{80}$${\mathrm{Ta}}_{20}$ and ${\mathrm{Ni}}_{75}$${\mathrm{Ta}}_{25}$ multilayers at different irradiation stages, and a fcc MC phase was formed in the Ta-rich ${\mathrm{Ta}}_{65}$${\mathrm{Ni}}_{25}$ and ${\mathrm{Ta}}_{75}$${\mathrm{Ni}}_{35}$ multilayers before and after the films were amorphized, respectively. Interesting evolution behavior of the above nonequilibrium solid phases upon thermal annealing was also observed. A free-energy diagram of the system was constructed based on the model of Miedema, de Boer, and de Boer and the method of Alonso and Simozar. The calculation included the free-energy curves of all the competing phases, especially the MC phases, which were considered as compoundlike, and the enthalpies were calculated based on well-identified structural parameters. The calculated energy sequence of the phases was verified at certain compositions by the phase appearance order in the respective as-deposited multilayers upon steady-state thermal annealing, thus confirming the relevance of the diagram in its general outline. The free-energy diagram can explain the formation and the thermal stability of the above solid phases. The growth kinetics of the hcp and fcc MC phases were also discussed in terms of the structural compatibility between the newly formed phase and the matrix in the ion-irradiation process.

Thermodynamic analysis of the Ni-Ta system.

The thermodynamic properties of the solution and compound phases of the Ni-Ta system were optimized using experimental information on phase diagram and thermochemical quantities. A consistent set of parameters is presented.