Ti Hf Alloys Research Articles

Thermodynamic modeling of the Ni–Ti–Hf system

Ni–Ti–Hf alloys have received extensive attention owing to their excellent shape-memory behavior. In the present work, the thermodynamic assessment of the Ni–Ti–Hf system was performed using the CALPHAD method after a critical review of the thermodynamic descriptions of boundary binaries and available experimental data in the ternary system. The solubility ranges of the third elements in binary intermetallic compounds are well described. Moreover, the wide homogeneity ranges of the B2 and NiTi2 phases are satisfactorily reproduced. The ternary τ phase was reasonably described using a two-sublattice model (Ni)0.44(Hf,Ti)0.56. Both the thermochemical properties and phase diagrams were well described using the present model parameters.

Surface tension measurement of Ti–Zr and Ti–Hf alloys at high-temperature by the pendant drop method

High-temperature alloy melts introduced into carbon/carbon (C/C) composites by reactive melt infiltration (RMI) to form ultra-high-temperature ceramics (UHTCs) is currently an important method for improving their ablation resistance. As a fundamental thermo-property, surface tension has an important impact on the infiltration of alloy melts into the C/C composites. However, the surface tension of binary alloy systems, such as Ti–Zr and Ti–Hf, used for RMI has been little studied. In this work, experimental measurements through the pendant drop method and theoretical calculations of the surface tension of Ti–Zr and Ti–Hf alloys with different compositions have been carried out. Meanwhile, inevitably, impurities are introduced during the determination of surface tension at high temperatures, mainly carbon and oxygen. The effect of impurities on the phase composition, distribution, and surface tension of the alloys is investigated. The results demonstrated that the experimental measurements are in good agreement with the theoretical values of Butler's equation. The surface tension of Ti–Zr and Ti–Hf alloys increases with the content of Zr or Hf at the same temperature. Small amounts of oxygen are mainly dissolved in the lattice and have no significant effect on the surface tension. Carbon slightly decreases the surface tension of the alloy.

Mixing enthalpy of the Co–Ti–Hf liquid alloys and regularities of the function change in the row of the ternary (Co, Ni, Cu)–Ti–Hf glass-forming melts

The partial molar mixing enthalpies of titanium and hafnium in liquid Co–Ti–Hf alloys were studied at 1900 K by high-temperature isoperibolic calorimetry along xCo/xHf = 3 and xCo/xHf = 3 sections. The partial mixing enthalpies of undercooled liquid titanium and hafnium in liquid alloys and the integral mixing enthalpy are negative over the studied composition range. The thermodynamic mixing functions of liquid (Co, Ni, Cu)–Ti–Hf alloys were modeled in the framework of the associate solution model. Regularities in the change of thermodynamic mixing functions in liquid glass-forming (Co, Ni, Cu)–Ti–Hf alloys are discussed considering donor–acceptor interaction of the components in the melts.

High-Temperature Cermet Material Based on Intermetallic Nickel Matrix

A method for synthesis of an intermetallic nickel matrix reinforced with particles of different refractory compounds added at different concentrations is considered. Prepared materials are based on two variants of a Ni3Al–Cr–W–Mo–Ti–Hf alloy: type VKNA-1V alloy and type VKNA-1V alloy with increased tungsten content (VKNA-1V(W)). The intermetallic matrix is reinforced with nanoparticles of the oxides Al2O3, Al2O3 ⋅ Y2O3, and Al2O3 ⋅ Y2O3 ⋅ HfO2, with the content of reinforcing component at 2 and 5 vol %. Samples are compacted by spark plasma sintering. The microstructure of prepared cermet materials (CMs) is investigated using scanning electron microscopy. The impact viscosity and flexural strength are determined. We establish the effect that the content and composition of the reinforcing component has on the physicomechanical properties of the high-temperature CMs based on an intermetallic matrix dispersion-hardened with refractory metal particles. Our findings show that the optimal combination of flexural strength and impact viscosity at room temperature is achieved in the CM sample in which the intermetallic matrix is based on VKNA-1V(W) alloy and the reinforcing component is represented by ternary oxide Al2O3 ⋅ Y2O3 ⋅ HfO2 added at a concentration of 2%.

Development of hafnium metal and titanium-hafnium alloys having apatite-forming ability by chemical surface modification.

Hafnium (Hf) has attracted considerable attention as a component of biomedical titanium (Ti) alloys with low Young's moduli and/or shape-memory functionalities, because its cytotoxicity is as low as that of Ti. The drawback of metals is that their bone-bonding ability is generally low. It is known that apatite formation in the body is a prerequisite for bone-bonding. Although several chemical treatments have been proposed for preparing Ti for bone-bonding, there have been no similar investigations for Hf. In the present study, NaOH- and heat-treatments were applied to pure Hf and Ti-Hf alloys and their bone-bonding ability was assessed in vitro with the use of simulated body fluid (SBF). After NaOH- and heat-treatments, anatase formed on alloys with low Hf content (20-40% (atom%) Hf); mixtures of sodium titanate and hafnium titanate formed on alloys with similar Ti and Hf content (60% Hf); and hafnium oxide formed on alloys with high Hf content (80% Hf and pure Hf). Precipitates of apatite were observed on all the metals in SBF, except for the alloy with 60% Hf. We speculated that the hafnium titanate formed on this alloy had a low apatite-forming ability owing to its high negative surface charge, which inhibited P adsorption. The apatite-forming abilities of the Ti-Hf alloys strongly depended on their Hf content. The present results indicate that Hf-based materials have good potential for bone-bonding. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2519-2523, 2018.

Structure and thermoelastic martensitic transformations in ternary Ni–Ti–Hf alloys with a high-temperature shape memory effect

The effect of alloying by 12–20 at % Hf on the structure, the phase composition, and the thermoelastic martensitic transformations in ternary alloys of the quasi-binary NiTi–NiHf section is studied by transmission electron microscopy, scanning electron microscopy, electron diffraction, and X-ray diffraction. The electrical resistivity is measured at various temperatures to determine the critical transformation temperatures. The data on phase composition are used to plot a full diagram for the high-temperature thermoelastic B2 ↔ B19’ martensitic transformations, which occur in the temperature range 320–600 K when the hafnium content increases from 12 to 20 at %. The lattice parameters of the B2 and B19’ phases are measured, and the microstructure of the B19’ martensite is analyzed.

Atomistic modeling of ternary additions to NiTi and quaternary additions to Ni–Ti–Pd, Ni–Ti–Pt and Ni–Ti–Hf shape memory alloys

The behavior of ternary and quaternary additions to NiTi shape memory alloys is investigated using a quantum approximate method for the energetics. Ternary additions X to NiTi and quaternary additions to Ni–Ti–Pd, Ni–Ti–Pt, and Ni–Ti–Hf alloys, for X=Au, Pt, Ir, Os, Re, W, Ta,Ag, Pd, Rh, Ru, Tc, Mo, Nb, Zr, Zn, Cu, Co, Fe, Mn, V, Sc, Si, Al and Mg are considered. Bulk properties such as lattice parameter, energy of formation, and bulk modulus of the B2 alloys are studied for variations due to the presence of one or two simultaneous additives.

Effect of hydrogen on the structure of alloys formed in the Ti-Zr-Hf-H system

Investigated was the crystal structure of the Ti-Zr, Ti-Hf, and Ti-Zr-Hf alloys prepared by the novel method of “hydride cycling” suggested by us recently. The XRD data showed formation of the ω-phase in alloys with hydrides ratios TiH2/ZrH2 (TiH2/HfH2) ≈ 2, 1, 0.44: Ti0.67Zr0.33 (Ti2Zr), Ti0.67Hf0.34 (Ti2Hf), etc. The ω-phase is unusual for binary Ti-Zr and Ti-Hf alloys at normal pressure. The SHS reaction of α- and ω-alloys with hydrogen was found to yield complex hydrogen-rich hydrides with a fcc or bct structure such as Ti0.9Zr0.1H1.9, Ti0.677Zr0.33H1.81, Ti0.5Zr0.5H1.37, and Ti0.3Zr0.7H1.96.

Effects of TiN film coating on electrochemical behaviors of nanotube formed Ti- xHf alloys

Ti- xHf ( x=10%, 20%, 30% and 40%, mass fraction) alloys were prepared by arc melting, and the microstructure was controlled for 24 h at 1 000 °C in argon atmosphere. The formation of nanotube was conducted by anodizing on Ti-Hf alloys in 1.0 mol/L H 3PO 4 electrolytes with small amounts of NaF at room temperature. And then TiN coatings were coated by DC-sputtering on the anodized surface. Microstructures and nanotube morphology of the alloys were examined by field emission scanning electron microscopy(FE-SEM) and X-ray diffractometry(XRD). The corrosion properties of the specimens were examined through potentiodynamic test (potential range from −1 500 to 2 000 mV) in 0.9 % NaCl solution by potentiostat. The microstructure shows the acicular phase and α′ phase with Hf content. The amorphous oxide surface is transformed to crystalline anatase phase. TiN coated nanotube surface has a good corrosion resistance.

Surface characteristics of HA coated Ti-Hf binary alloys after nanotube formation

Ti-Hf binary alloys contained 10%, 20%, 30% and 40% (mass fraction)Hf were manufactured in the vacuum furnace system. And then, specimens were homogenized for 24 h at 1 000 °C in argon atmosphere. The formation of oxide nanotubes was conducted by anodic oxidation on the Ti-Hf alloy in 1 mol/L H 3PO 4 electrolytes containing small amounts of NaF at room temperature. The hydroxyapatite (HA) coating made of tooth ash prepared by electron-beam physical vapor deposition (EB-PVD) method. The corrosion behaviors of the specimens were examined through potentiodynamic test in 0.9% NaCl solution by potentiostat. The microstructures of the alloys were examined by field emission scanning electron microscopy (FE-SEM) and x-ray diffractometer (XRD). It was observed that the lamellar structure translated to needle-like structure with Hf contents. Nanotube formed and HA coated Ti- xHf alloys had a good corrosion resistance.

Passive films and corrosion resistance of Ti–Hf alloys in 5% HCl solution

Ti–Hf alloys with Hf contents of 10, 20, 30, and 40 mass% were prepared by a tri-arc furnace and homogenized at 1273 K for 21.6 ks, and then these alloys were cold rolled into 3-mm-thick plates. The alloy specimens were subjected to a solution treatment in a vacuum at 1223 K for 3.6 ks and then rapidly quenched in ice water before corrosion tests. The corrosion resistance of these alloys was investigated by studying the anodic polarization curves at 310 K in 5% HCl solution to determine the potential use of these alloys in biomedical applications. The passive films formed on the surfaces of the alloys were examined by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. The results reveal that all the Ti–Hf alloys exhibit a passive behavior in 5% HCl solution, which is attributed to the passive film formation of a mixture of both HfO 2 and TiO 2. The corrosion resistance of the Ti–Hf alloys gently increases with the Hf content and the Ti–Hf alloys exhibit better corrosion resistance than commercial pure (CP) Ti—the currently-used metallic biomaterial.

Nanotube formation and morphology change of Ti alloys containing Hf for dental materials use

In this paper, Ti–Hf (10, 20, 30 and 40 wt.%) alloys were prepared by arc melting, and subjected to heat treatment for 24 h at 1000 °C in an argon atmosphere. Formation of surface nanotubes was achieved by anodizing a Ti–Hf alloy in 1.0 M H 3PO 4 electrolytes with small amounts of NaF at room temperature. Microstructures of the alloys and nanotube morphology were examined by field-emission scanning electron microscopy (FE-SEM) and X-ray diffraction (XRD). The homogenized Ti–Hf alloys had a needle-like microstructure of α phase, and nanotubes formed on Ti– xHf alloys had the anatase phase after treatment that promoted crystallization. Uniform nanotubes formed for Hf contents up to 20 wt.%. Irregular nanotubes formed on the Ti–30Hf and Ti–40Hf alloys. The structure of the irregular layers on the Ti–30Hf and Ti–40Hf alloys had nanotubes of two sizes. Increasing the Hf content in Ti led to the formation of nanotubes with more narrow size. The pores in the nanotubes typically had a diameter ranging from 80–120 nm and a length of approximately 1.7 μm. It is concluded that nanotube morphology on Ti–Hf alloys can controlled by varying the amount of Hf.

Biocompatibility of uncoated and diamond-like carbon coated Ti–20%Hf alloy

Biocompatibilities of uncoated and diamond like carbon (DLC) coated Ti–20%Hf alloy have been investigated by means of 3T3 mouse fibroblast cell viability quantification using flow cytometry. For comparison, similar tests were performed for pure Ti, Hf, and V as well as a commercial orthopaedic alloy, Ti–6Al–4V. Under the test conditions used, the biocompatibilities of uncoated and DLC coated Ti–20%Hf alloy, pure Hf, and Ti–6Al–4V alloy were comparable to that of pure Ti, a metal known for its superior biocompatibility, while pure V clearly exhibited the lowest biocompatibility of all the materials that were evaluated. The addition of Hf to Ti resulted in significant solid solution strengthening and at 20%Hf concentration the hardness of this alloy was comparable to that of the Ti–6Al–4V alloy. Ti–Hf alloys and wear resistant, low friction DLC coatings may either be used in conjunction with or may independently hold promise for orthopaedic implants and possibly other biomedical applications.

Electrochemical Properties of TiN and ZrN Coated Ti-Hf Alloy

The Ti-Hf alloy system forms α-β isomorphous system and does not form any intermetallic compounds, which is also beneficial for good mechanical properties. And in order to avoid the release of materials, surface modifications are generally carried out to form a TiN and ZrN layer on the surface. Electrochemical properties of TiN and ZrN coated Ti-Hf alloy by RFsputtering has been researched using various electrochemical methods. Ti-10wt%, 20wt%, 30wt%, and 40wt% Hf alloys manufactured by non consumable vacuum arc melting furnace. All the specimens were heat treatment at 1000°C for 24hr in Ar atmosphere followed by furnace cooling, respectively. The specimens were coated with TiN and ZrN respectively, by RF-magnetron sputtering method. The microstructures were conducted by using OM, EDX and SEM. The corrosion tests were carried out using potentiodynamic(PARSTAT 2273, EG&G, USA) and potentiostatic test in 0.9% NaCl solution at 36.5 ±1 °C. Microstructure clearly observed that lamellar structure translated to needle-like structure with increased Hf contents. From the analysis of TiN and ZrN coated layer analysis, TiN and ZrN coated surface showed columlar structure with 600nm and 100nm thickness, respectively. The corrosion resistance of TiN and ZrN coated Ti alloys were higher than those of the non-coated Ti-alloy in 0.9%NaCl solution, indicating better protective effect.

Changes in mechanical properties of Ti alloys in relation to alloying additions of Ta and Hf

Abstract The effects of Ta and Hf on the dynamic Young's moduli and tensile properties of Ti–Ta and Ti–Hf alloys for biomedical applications are comparatively studied in this paper. It is found that with increasing Hf content, the dynamic Young's modulus of the Ti–Hf alloy gently decreases and its tensile strength keeps on increasing. In contrast, with increasing Ta content, the dynamic Young's modulus of the Ti–Ta alloys first decreases, reaches a minimum value of 69 GPa and then increases. In parallel, the tensile strength first increases, reaches a maximum value of 587 MPa, and then slightly decreases. It is shown that the addition of Hf has a slight influence on the dynamic Young's modulus and a strong influence on the tensile properties of the Ti–Hf alloy, while an increase of Ta content has a strong effect on both the dynamic Young's modulus and tensile properties of the Ti–Ta alloy.

Effects of Ni, Ti and Hf on the glass forming ability of the Ni–Ti–Hf ternary alloys

Under the framework of the second-moment approximation of tight-binding model, a relevant potential with a binomial-truncated function proposed by the present authors is developed for Ni–Ti–Hf ternary system. Based on the newly constructed Ni–Ti–Hf potential, molecular dynamics (MD) simulations upon solid solution models predict that the glass forming ranges of Ni–Ti and Ni–Hf systems are 32–87 at.% of Ti and 20–85 at.% of Hf, respectively, and that Ti and Hf cannot form amorphous alloys in whole composition. Importantly, the predicted results are in a good agreement with the results derived from other theoretical methods and the experimental observations. Meanwhile, the effects of Ni, Ti, and Hf, respectively, on the glass forming ability (GFA) of the Ni–Ti–Hf alloys also have been predicted by MD simulations based on the constructed Ni–Ti–Hf ternary potential. The simulated results reveal that Ni and Hf can improve the GFA of Hf(Ti)-based and Ni-based Ni–Ti–Hf ternary alloys, respectively, while Ti will reduce the GFA of Ni-based Ni–Ti–Hf alloys, which also match well with the experimental observations and are in accordance with some proposed empirical models.

Effects of heat treatment on the microstructure of Ti-Hf alloy.

Effects of heat treatment on the microstructure of Ti-Hf alloy.

Grindability of cast Ti–Hf alloys

As part of our systematic studies characterizing the properties of titanium alloys, we investigated the grindability of a series of cast Ti-Hf alloys. Alloy buttons with hafnium concentrations up to 40 mass% were made using an argon-arc melting furnace. Each button was cast into a magnesia-based mold using a dental titanium casting machine; three specimens were made for each metal. Prior to testing, the hardened surface layer was removed. The specimens were ground at five different speeds for 1 min at 0.98 N using a carborundum wheel on an electric dental handpiece. Grindability was evaluated as the volume of metal removed per minute (grinding rate) and the volume ratio of metal removed compared to the wheel material lost (grinding ratio). The data were analyzed using ANOVA. A trend of increasing grindability was found with increasing amounts of hafnium, although there was no statistical difference in the grindability with increasing hafnium contents. We also found that hafnium may be used to harden or strengthen titanium without deteriorating the grindability.

Electrochemical characterization of cast Ti–Hf binary alloys

This study characterized the electrochemical behavior of Ti–Hf binary alloys in a simulated oral environment. Ti–Hf alloys (10, 20, 25, 30, 35 and 40 mass% Hf) were prepared by arc-melting titanium sponge and hafnium sponge. Specimens of each alloy ( n = 4) were prepared using a dental titanium casting system with a MgO-based investment. Specimens were inspected with X-ray radiography to ensure minimal internal porosity. Castings ( n = 4) made from pure titanium and commercially pure titanium were used as controls. The ground flat surface (10 mm × 10 mm) on each specimen where approximately 30 μm was removed was used for the characterization. Sixteen-hour open-circuit potential (OCP) measurement, linear polarization and potentiodynamic cathodic polarization were performed sequentially in aerated (air + 10% CO 2) MTZ synthetic saliva at 37 °C. Potentiodynamic anodic polarization was conducted in the same medium but deaerated (N 2 + 10% CO 2) 2 h before and during testing. Polarization resistance ( R P) and Tafel slopes were determined, as were corrosion current density ( I CORR) and passive current density ( I PASS). Results were subjected to nonparametric statistical analysis ( α = 0.05). The OCP stabilized (mean values −229 mV to −470 mV vs. SCE) for all specimens after the 16-h immersion. Similar passivation was observed for all the metals on their anodic polarization diagrams. The Kruskal–Wallis test showed significant differences in OCP among the test groups ( p = 0.006). No significant differences were found in R P, I CORR or I PASS among all the metals ( p > 0.3). Results indicate that the electrochemical behavior of the Ti–Hf alloys examined resembles that of pure titanium.

Mechanical properties of cast Ti-Hf alloys

This study examined the mechanical properties of a series of Ti-Hf alloys. Titanium alloys with 10 to 40 mass % Hf were made with titanium and hafnium sponge in an argon-arc melting furnace. Specimens cast into magnesia-based investment molds were tested for yield strength, tensile strength, percentage elongation, and modulus of elasticity. Vickers microhardness was determined at 25 to 600 microm from the cast surface. X-ray diffractometry was also performed. Commercially pure Ti (CP Ti) and pure Ti prepared from titanium sponge were used as controls. The data (n = 5) were analyzed with a one-way ANOVA and the Student-Newman-Keuls test (alpha = 0.05). The diffraction peaks of all the metals matched those for alpha Ti; no beta phase peaks were found. Alloys with Hf > or = 25% had significantly (p < 0.05) higher yield and tensile strength compared to the CP Ti and pure Ti. There were no significant differences (p > 0.05) in elongation among all the Ti-Hf alloys and CP Ti, whereas the elongation of alloys with Hf > or = 30% was significantly (p < 0.05) lower than that of the pure Ti. The cast Ti-Hf alloys tested can be considered viable alternatives to CP Ti because they were stronger than CP Ti and had similar elongation.