Hf Ni Alloys Research Articles

Effect of Hf on the lattice invariant shear and self-accommodation of martensite in Ti–Ni–Hf alloys

Effect of Hf on the lattice invariant shear and self-accommodation of martensite in Ti–Ni–Hf alloys

Interaction of the components in liquid glass-forming Fe–Hf–Ni alloys

The enthalpies of mixing of liquid Fe–Hf–Ni alloys were studied at 1873 K by means of a high-temperature isoperibolic calorimeter. The investigations were performed along the section xFe/xNi = 3/1 at xHf = 0–0.18 and sections xFe/xNi = 1/1 and 1/3 at xHf = 0–0.46. The limiting partial enthalpies of mixing of undercooled liquid hafnium in liquid Fe–Ni alloys are (–135 ± 10) kJ mol−1 (at xFe/xNi = 3/1), (–155 ± 14) kJ mol−1 (at xFe/xNi = 1/1), and (–203 ± 15) kJ mol−1 (at xFe/xNi = 1/3). The integral mixing enthalpies are negative over the studied composition range. The integral mixing enthalpies show negative deviations from ideal mixing in the entire composition range. The thermodynamic properties of liquid ternary alloys are modeled using the associate solution model. The amorphization range in the ternary system is predicted by considering a total molar fraction of associates in undercooled liquid alloys.

Metastable phases and nanocrystalline-forming ability (NFA) of melt-quenched Ni-rich (Zr, Hf)–Ni alloys

Abstract In this paper, the basic principles of and some recent advances in rapid solidification are briefly considered, with main emphasis on the formation of single-phase metastable states during meltquenching in Ni-rich Zr –Ni and Hf–Ni alloys. Factors controlling nanocrystalline-forming ability are discussed in detail, with particular view on the preparation of single-phase nanocrystalline alloys by the melt-quenching process.

Calorimetric Investigation of the Mixing Enthalpy of Liquid Hf-Ni-Ti Alloys and Thermodynamic Properties and Chemical Ordering in Quaternary Liquid Cu-Hf-Ni-Ti Alloys

The mixing enthalpies of liquid Hf-Ni-Ti alloys were measured at 1873 K by applying a high-temperature isoperibolic calorimeter. The investigation was performed along the xHf/xNi = 3 section at xTi = 0-0.64 and along the xNi/xTi = 3 section at xHf = 0-0.57. The limiting partial enthalpy of mixing of undercooled liquid titanium in liquid Hf-Ni alloy is (− 92 ± 15) kJ mol−1. The partial enthalpy of mixing of undercooled liquid hafnium at infinite dilution is (− 163 ± 12) kJ mol−1. The integral mixing enthalpies are negative nearly in the entire composition range. The thermodynamic properties of liquid quaternary alloys are modelled using the associate solution model. The amorphization ranges in ternary and quaternary systems are predicted by considering a total molar fraction of associates in liquid alloys.

The structural features of the amorphous C14 HfNiAl Laves phase

Purpose: In order to clarify whether amorphization occurs in the pseudo-binary C14 HfNi0.6Al1.4 Laves phase a detailed investigation of the effect of hydrogen treatment on it phase-structural state has been studied. This type of compounds is of interest due to their high possibility to hydrogen absorption as Laves phase structures and as Hf-Ni alloys. Design/methodology/approach: We used a combination of hydrogen treatment and grinding methods for studying of the processes of controlled structure formation. High temperature transformations of the HfNi0.6Al1.4 alloy were pointed out by means of XRD analysis. Findings: By combination of two amorphization methods and high temperature measurements we have observed a phase structural transformation of the HfNi0.6Al1.4 alloy, which could be presented as: HfNi0.6Al1.4(cryst.) + H2 ® HfNi0.6Al1.4 (nanocryst.) + HfNi0.6Al1.4 (amorphous) + H2 ® HfH2 (amorphous) + AlH3 (amorphous) + Ni. Ferromagnetic- like properties of the pseudo-binary HfNi0.6Al1.4 Laves phase was found. Research limitations/implications: Complex research of HfNi0.6Al1.4 alloy revealed various structure features depending on phase content, thermodynamic parameters and conditions of hydrogen treatment. Obtained results suppose that further studies of structure and physical properties of Hf-Ni-Al alloys will allow to find the methods to control the producing of materials with desired properties. Practical implications: Using of hydrogen treatment is effective to produce Al-based alloys with improved magnetic properties. Originality/value: Treatment in hydrogen atmosphere allows improving the glass-forming ability in Hf-Ni-Al alloys.

Local structure evolutions of metallic glasses during shear deformation investigated by computer simulations

Based on the experimental data and first-principle calculations, the newly constructed long-range empirical potential was first developed for the Ni-Hf-Mo system. Taking the realistic interatomic potential as the starting point, the atomic-level structure and its correlation with the shear deformation process of the Ni-Hf-Mo metallic glasses were investigated and characterized by atomic simulations and various analysis methods. Interestingly, the appropriate amount of Mo addition to Ni-Hf alloys could enhance the intrinsic strength, while reducing the plasticity. By monitoring atomic-scale structure during the shear deformation, local shear behaviors are closely correlated with the structural and mechanical response. In addition, the connectivity degree of the spatial network could have a considerable effect on the structure and performance of metallic glasses.

Mixing enthalpy of liquid Cu–Hf–Ni alloys at 1873 K

The mixing enthalpies of liquid Cu–Hf–Ni alloys were determined at 1873 K by applying a high-temperature isoperibolic calorimeter. The investigation was performed along the sections xCu/xNi = 3/1, 1/3 at xHf = 0–0.45 and xCu/xNi = 1/1 at xHf = 0–0.40. The limiting partial mixing enthalpies of undercooled liquid hafnium in liquid Cu–Ni alloys are (–158 ± 13) kJ mol−1 (section xCu/xNi = 3/1), (–213 ± 11) kJ mol−1 (section xCu/xNi = 1/1), and (–229 ± 11) kJ mol−1 (section xCu/xNi = 1/3). The integral mixing enthalpies are negative in a wide composition range. The Redlich–Kister–Muggianu polynomial was used for the least square fit of the experimental results to obtain an analytical expression for the integral mixing enthalpy.

Structural Transformations and Thermal Expansion in Aluminum Alloys of the Al–Ni–Zr and Al–Ni–Hf Systems

We study the structural transformations in Al–Ni–Zr and Al–Ni–Hf alloys in the concentration regions with high contents of Al. The eutectoid transformation of the Zr6Ni8Al15 phase into a microscopic mixture of compounds NiAl + ZrNi0.5Al1.5 and the peritectic formation of HfNi0.35Al1.65 from a mixture of HfNi2Al5 and Hf6Ni8Al15 are discovered. The temperature dependence of the structural parameters is analyzed and the thermal expansion coefficient for the HfNi0.35Al1.65 phase is found within the range 393–723°K.

Fermi level tuning using the Hf-Ni alloy system as a gate electrode in metal-oxide-semiconductor devices

Hf-Ni alloys are studied as a gate electrode for metal-oxide-semiconductor devices. The Hf-Ni solid-state amorphization couple encompasses several metallurgical phenomena which are investigated at the nanoscale and are correlated with the macroscopic electrical properties of devices. The dependence of the Fermi level position on the alloy composition is studied both on SiO2 and on HfO2. In order to isolate the effects of interfacial and dielectric charges and dipoles, the dependence of the vacuum work-function values on the composition is also studied. The Fermi level positions of the alloys do not depend linearly on the average composition of the alloys and are strongly affected by Hf enrichment at the HfNix/dielectric interface and the HfNix surface. We note a constant shift of 0.4 eV in the Fermi level position on HfO2 compared to SiO2. In addition, characterization of the composition, structure, and morphology reveals Kirkendall voids formation when the bottom layer consists of Ni, and an oxygen-scavenging effect when the bottom layer is Hf.

Thermodynamic properties of liquid alloys of the Ni-Hf system

By the method of calorimetry in isoperibolic conditions are determined integral and partial mixing enthalpies of liquid alloys of the Ni-Hf system at 1770 ± 5 K. Defined that liquid Ni-Hf alloys are formed with allocated large quantity of heat. The analysis of own and literary data has allowed to establish for mixing enthalpies of binary Ni-Hf liquid alloys dependence on temperature. With use of the Schroder equation are calculated the activities of studied alloys components from co-ordinates of liquidus line of the phase diagram of this system. Between calculated and experimentally established values of melts components activities of the Ni-Hf system is observed only qualitative consent. Are also calculated ΔG and ΔS of liquid Ni-Hf alloys.

The time differential perturbed angular correlation study of the Ni–5 at.% Hf alloy

The time differential perturbed angular correlation technique was used to observe the magnetic dipole and electric quadrupole interactions of 181Ta probe in the Ni–5 at.% Hf alloy from 78 to 1131 K. The presence of the Larmor precession frequency of 181Ta in the Ni(Hf) solid solution phase confirms the Ni dominant concentration for the onset of ferromagnetism in the Ni–Hf alloys. A very weak quadrupole interaction originates from imperfections in the HfNi 5 phase formed during melting procedure. The third observed quadrupole interaction corresponds to the Ta probe in the HfO 2 contamination due to internal oxidation of the sample.

Hyperfine magnetic field at Ta impurities in nickel: Perturbed angular correlation and first principle calculation study

The hyperfine magnetic field ( H h f ) in 0.2 at.% Hf–Ni alloy is measured at the 181Ta probe using the time-differential perturbed angular correlation (TDPAC) method, in the temperature range 78–675 K. The obtained value of 8.6 (3) T at room temperature is in good agreement with the previously reported measurements for similar Hf concentrations in Ni. X-ray powder diffraction (XRPD) experiments confirmed that small atomic concentrations of Hf atoms (<1 at.%) mainly substitute on Ni lattice sites in the fcc crystal lattice without forming any intermetallic phase. In addition, ab-initio calculation using all-electron augmented plane waves plus local orbitals (APW+lo) formalism is performed and the obtained result for the hyperfine magnetic field at Ta site is in accordance with the measurement.

Icosahedral ordering in Ti–Hf–Ni alloys?

The local atomic structure of crystalline and amorphous Ti–Hf–Ni alloys has been probed by EXAFS. The local order is similar in the crystalline Ti–Hf–Ni alloy and in Ti–Zr–Ni crystalline and quasicrystalline phases, where icosahedral ordering exists around some nickel sites. The local atomic structure is different in the amorphous Ti–Hf–Ni alloys, in particular around the nickel atoms, where a new icosahedral atomic configuration that is similar to that in the Ti2Ni crystal phase is identified.

Hydrogen solution properties in a series of amorphous Zr–Hf–Ni alloys at elevated temperatures

Amorphous alloys are anticipated as new membrane materials for high purity hydrogen production, as substitutes for expensive palladium alloys. For amorphous Zr–Ni-based alloys reported to date, hydrogen permeability increases with Zr content. Hydrogen solution properties in a series of amorphous Zr–Hf–Ni ternary alloys were measured carefully using the Sieverts method and residual hydrogen measurements to investigate the reason. Results indicate that hydrogen solubility in the ternary alloys increases with increasing Zr to improve hydrogen permeability, not because of the geometrical atomic structure but because of higher hydrogen affinity of Zr than that of Hf. Increased permeability with Zr in other amorphous Zr–Ni-based alloys is also expected to be attributable to the same reason. Additionally, hydrogen was found with low mobility, and was not removable even after 10 h evacuation at 573 K; the importance of decreasing low mobility hydrogen as a countermeasure against hydrogen embrittlement was pointed out. Equilibrium hydrogen concentration was found not to obey Sieverts’ law with respect to hydrogen pressure. Rather, it was linear roughly to the quarter power. Parameters to reproduce pressure–composition isotherms were determined using Kirchheim's theory.

Glass-forming ability and stability of ternary Ni-early transition metal (Ti/Zr/Hf) alloys

Four Ni-bearing Ti, Zr and Hf ternary alloys of nominal composition Zr 41.5Ti 41.5Ni 17, Zr 25Ti 25Ni 50, Zr 41.5Hf 41.5Ni 17 and Ti 41.5Hf 41.5Ni 17 were rapidly solidified in order to produce ribbons. The Zr–Ti–Ni and Ti–Hf–Ni alloys become amorphous, whereas the Zr–Hf–Ni alloy shows precipitation of a cubic phase. The devitrification of all three alloys was followed and the relative tendency to form nanoquasicrystals and cF96 phases analysed. The relative glass-forming ability of the alloys can be explained by taking into account their atomic size difference. Addition of Ni often leads to quasicrystallisation or quasicrystal-related phases. This can be explained by the atomic radius and heat of mixing of the constituent elements. The phases precipitated at the initial stages of crystallisation indicate the possible presence of Frank–Kasper polyhedral structure in the amorphous alloys. Structural analysis reveals that the Laves and the anti-Laves phases have the same polyhedral structural unit, which is similar to the structural characteristics of glass.

ORDERING BEHAVIOR OF FCC AND HCP ALLOYS IN Ni-Hf AND Re-Ti SYSTEMS

The concentration dependence of atomic short range order (SRO) has been studied in Ni 100-x Hf x and Re 100-x Ti x alloys (where x = 2, 5, 10, 15, 20 at.%) using the framework of transition metal model pseudopotential (TMMP). The ordering energies and Warren–Cowley SRO parameters were calculated for the Ni-Hf and Re-Ti alloys. It was found that this model predicted the correct sign of SRO for Ni 100-x Hf x system but failed in the case of Re 100-x Ti x alloys.

SEM and XRD Characterization of Ni-Hf Alloys at Low Hf Concentration

The alloying and phase formation in Ni-Hf samples with 0.2-, 2-, and 5-at.% Hf were studied by X-ray diffraction (XRD) technique and scanning electron microscopy (SEM). Both characterization methods, XRD and SEM, reveal the presence of the HfNi5 phase (fcc structure) where the excess Ni atoms are present in the form of Ni or Ni-rich segregations in the sample containing 5-at.% Hf. The sample with 2-at.% Hf is characterized by the presence of the two phases present in the 5-at.% sample and by Hf atoms, which occupy substitutional lattice positions in the Ni lattice. Finally, in the third sample with 0.2-at.% Hf, the Hf atoms mainly substitute the Ni atoms in the lattice. This analysis is being complemented with additional information on the local structure around Hf by extended X-ray absorption fine structure spectroscopy (EXAFS).

Phase transformation and precipitation in aged Ti–Ni–Hf high-temperature shape memory alloys

More attention has been paid to ternary Ti–Ni–Hf high-temperature shape memory alloys (SMAs) due to their high phase transformation temperatures, good thermal stability and low cost. However, the Ti–Ni–Hf alloys have been found to have low ductility and only about 3% shape memory effect and these have hampered their applications. It is well known that there are three methods to improve the shape memory properties of high-temperature SMAs: (a) cold rolling + annealing; (b) adding another element to the alloy; (c) aging. These methods are not suitable to improve the properties of Ti–Ni–Hf alloys. In this paper, a method of conditioning Ni-rich Ti–Ni–Hf alloys as high-temperature SMAs by aging is presented. For Ni-rich Ti 80− x Ni x Hf 20 alloys (numbers indicate at.%) the phase transformation temperatures are on average increased by more than 100 K by aging at 823 K for 2 h. Especially for those alloys with Ni contents less than 50.6 at.%, the martensitic transformation start temperatures (M s) are higher than 473 K after aging. Transmission electron microscopy shows the presence of (Ti + Hf) 3Ni 4 precipitates after aging. Compared with the precipitation of Ti 3Ni 4 particles in Ni-rich Ti–Ni alloys, the precipitation of (Ti + Hf) 3Ni 4 particles in Ni-rich Ti–Ni–Hf alloys needs higher temperatures and longer times.

Metastable phases and nanocrystalline-forming ability (NFA) of melt-quenched Ni-rich (Zr,Hf)–Ni alloys

Abstract In this paper, the basic principles of and some recent advances in rapid solidification are briefly considered, with main emphasis on the formation of single-phase metastable states during meltquenching in Ni-rich Zr–Ni and Hf–Ni alloys. Factors controlling nanocrystalline-forming ability are discussed in detail, with particular view on the preparation of single-phase nanocrystalline alloys by the meltquenching process.

Structural transition and glass-forming ability of the Ni–Hf system studied by molecular dynamics simulation

A tight-binding Ni–Hf potential is constructed by fitting some of the ground-state properties, such as the cohesive energy, lattice constants, and the elastic constants of some Ni–Hf alloys. The constructed potential is verified to be realistic by reproducing some static and dynamic properties of the system, such as the melting points and thermal expansion coefficients for the pure Ni and Hf as well as some of the equilibrium compounds, through molecular dynamics simulation. Applying the constructed potential, molecular dynamics simulations are performed to compare the relative stability of the face-centered-cubic (fcc)/hexagonal close-packed (hcp) solid solutions to their disordered counterparts as a function of solute concentration. It is found that the solid solutions become unstable and transform into the disordered states spontaneously, when the solute concentrations exceed the two critical solid solubilities, i.e., 25 at.% Ni for hcp Hf-rich solid solution and 18 at.% Hf for fcc Ni-based solid solution, respectively. This allows us to determine that the glass-forming ability/range of the Ni–Hf system is within 25–82 at.% Ni. Interestingly, simulations also reveal for the first time, that two mixed regions exist in which an amorphous phase coexists with a crystalline phase, and at about 18 at.% Ni, the hcp lattice turns into a new metastable phase identified to be face-centered orthorhombic structure.