Interdiffusion and thermotransport in Ni–Al liquid alloys

In this paper, we present extensive self-consistent results of molecular dynamics (MD) simulations of diffusion and thermotransport properties of Ni–Al liquid alloys. We develop a new formalism that allows easy connection between results of the MD simulations and the real experiments. In addition, this formalism can be extended to the case of ternary and higher component liquid alloys. We focus on the temperature and composition dependence of the self-diffusion coefficients, interdiffusion coefficients, thermodynamic factor, Manning factor and the reduced heat of transport. The two latter quantities both represent measures of the off-diagonal Onsager phenomenological coefficients. The Manning factor and the reduced heat of transport can be related to experimentally obtainable quantities provided the thermodynamic factor is available. The simulation results for the reduced heat of transport show that for all compositions, in the presence of a temperature gradient, Ni tends to migrate to the cold end. This is in agreement with an available experimental study for a Ni_21.5Al_78.5 melt (only qualitative result is available so far).     

Magnetic Thermocouples Made of Co–Fe and Ni–Fe Permalloys

Technical Physics - Magnetized and unmagnetized Co–Fe and Ni–Fe alloys fabricated on a two-high casting installation in the form of thin flexible amorphous films are promising materials...     

Electronic structures of CO adsorbed Pt-skin surface on Pt–Co and Pt–Ni alloys

By using angle resolved photoemission spectroscopy, we investigate the electronic structures of Pt-skin layer of Pt–Co and Pt–Ni alloys with CO molecules on the surface. Measured Fermi surface maps and band dispersions reflect the signatures of chemical bonding between Pt-skin layer and CO molecules. Furthermore, the degree of chemical bonding strength of CO molecules, estimated from the energy shift of the participating bands, is found to be reduced on both Pt bimetallic alloys. Our results show how the surface band structure of Pt bimetallic alloys is modified with molecular orbitals of CO molecules on the surface, revealing the important role of the electronic structure in the determination of chemical properties of bimetallic alloys.     

X-ray photoelectron studies of changes in the electronic structure upon phase transitions in Co–Ni and Co–Fe alloys

The changes in the electronic structure of Co–Ni and Co–Fe systems upon phase transitions are studied. X-ray photoelectron study of the valence-band spectra and the parameters of the multiplet splitting of Co, Ni and Fe 3s spectra is carried out at different temperatures. It is established that the ordering–separation phase transition in Co–Ni alloys takes place in the temperature range of 600–700°C. As opposed to Co–Ni alloys, in the Fe–Co alloy, ordering–separation–ordering phase transitions are observed. High-temperature ordering of the Fe₅₀Co₅₀ alloy is observed above 1200°C. The transition from ordering to separation is shown to lead to changes in the d electron spectra of the valence band and in the parameters of the multiplet splitting of the 3s spectra.     

Determination of surface tension of liquid ternary Ni–Cu–Fe and sub-binary alloys

Experimental data in the literature are almost limited to determine the thermophysical properties of multicomponent complex alloys, especially due to the inability of laboratories to achieve the desired ideal conditions, due to the difficulty of protection from oxidation at high temperatures and other contamination at high temperatures, due to time and cost in laboratory studies. Due to these reasons, the theoretical data obtained in this subject is of great importance. In this study, a series of geometric and physical models, such as Chou’s general solution model (GSM), Muggianu’s Model, Kohler’s Model, Toop’s Model, Hillert’s Model, Guggenheim’s Model, Butler’s Model, Egry’s Model and ideal solution model for quasi-binary alloy system for Section A: Ni_{0.4(1 – x)}Cu_xFe_{0.6(1 – x)}. and Section B: (Ni_xCu_0.2Fe_{0.8 – x}) are used to calculate the surface tension-composition and surface tension-temperature curves of the Cu-Fe-Ni ternary liquid system are plotted. The data for this process is evaluated by means of an extended Redlich-Kister-Muggianu polynomial fit to the experimental values of the surface tensions of the binary liquid alloy systems. The obtained results for these models are also compared with the available data in the literature and relatively good agreements are observed. In addition, the surface segregation having important key factor in determining surface tension of the liquid alloy Ni-Fe-Cu has also been investigated in this work.     

Hume-Rothery electron concentration rule across a whole solid solution range in a series of gamma-brasses in Cu–Zn,Cu–Cd,Cu–Al,Cu–Ga,Ni–Zn and Co–Zn alloy systems

The aim of the present work is to examine if the Hume-Rothery stabilisation mechanism holds across whole solid solution ranges in a series of gamma-brasses with especial attention to the role of vacancies introduced into the large unit cell. The concentration dependence of the number of atoms in the unit cell, N, for gamma-brasses in the Cu–Zn, Cu–Cd, Cu–Al, Cu–Ga, Ni–Zn and Co–Zn alloy systems was determined by measuring the density and lattice constants at room temperature. The number of itinerant electrons in the unit cell, e/uc, is evaluated by taking a product of N and the number of itinerant electrons per atom, e/a, for the transition metal element deduced earlier from the full-potential linearised augmented plane wave (FLAPW)-Fourier analysis. The results are discussed within the rigid-band model using as a host the density of states (DOS) derived earlier from the FLAPW band calculations for the stoichiometric gamma-brasses Cu₅Zn₈, Cu₉Al₄ and TM₂Zn₁₁ (TM = Co and Ni). A solid solution range of gamma-brasses in Cu–Zn, Cu–Cd, Cu–Al, Cu–Ga and Ni–Zn alloy systems is found to fall inside the existing pseudogap at the Fermi level. This is taken as confirmation of the validity of the Hume-Rothery stability mechanism for a whole solute concentration range of these gamma-brasses. An exception to this behaviour was found in the Co–Zn gamma-brasses, where orbital hybridisation effects are claimed to play a crucial role in stabilisation.     

Solidification mechanism transition of liquid Co–Cu–Ni ternary alloy

We report a solidification mechanism transition of liquid ternary Co₄₅Cu₄₅Ni₁₀ alloy when it solidifies at a critical undercooling of about 344 K. When undercooling at ΔT<344 K, the solidification process is characterized by primary S (Co) dendritic growth and a subsequent peritectic transition. The dendritic growth velocity of S (Co) dendrite increases with the rise of undercooling. However, once ΔT>344 K, the solidification velocity decreases with the increase of undercooling. In this case, liquid/liquid phase separation takes place prior to solidification. The minor L₂ (Cu) droplets hinder the motion of the solidification front, and a monotectic transition may occur in the major L₁ phase. These facts caused by metastable phase separation are responsible for the slow growth at high undercoolings.     

Low-resistance and transparent Ni–Co solid solution/Au ohmic contacts to p-type GaN for green GaN-based light-emitting diodes

We report on the formation of low-resistance and transparent p-type ohmic contact for green GaN-based light-emitting diodes (LEDs) using Ni–Co solid solution(5 nm)/Au(5 nm) scheme. The as-deposited Ni–Co solid solution(5 nm)/Au(5 nm) contact shows nonlinear current–voltage (I–V$I\text{–}V$) characteristics. However, annealing the sample at 550 ^°C in air results in the formation of ohmic contacts with specific contact resistance of 6.5×10⁻⁴ Ω cm². The annealed sample shows light transmittance of 71.7% at a wavelength of 530 nm, which is better than that (64.9%) of oxidized Ni/Au contacts. Based on Auger electron spectroscopy and x-ray photoemission spectroscopy results, the annealing-induced improvement of the contacts is described and discussed.     

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 Ni and vacancy concentration on initial formation of Cu precipitate in Fe–Cu–Ni ternary alloys by molecular dynamics simulation

In the present work, the effects of Ni atoms and vacancy concentrations(0.1%, 0.5%, 1.0%) on the formation process of Cu solute clusters are investigated for Fe–1.24%Cu–0.62%Ni alloys by molecular dynamics(MD) simulations. The presence of Ni is beneficial to the nucleation of Cu precipitates and has little effect on coarsening rate in the later stage of aging. This result is caused by reducing the diffusion coefficient of Cu clusters and the dynamic migration of Ni atoms. Additionally, there are little effects of Ni on Cu precipitates as the vacancy concentration reaches up to 1.0%,thereby explaining the embrittlement for reactor pressure vessel(RPV) steel. As a result, the findings can hopefully provide the important information about the essential mechanism of Cu cluster formation and a better understanding of ageing phenomenon of RPV steel. Furthermore, these original results are analyzed with a simple model of Cu diffusion, which suggests that the same behavior could be observed in Cu-containing alloys.     

X-ray fluorescence analysis of Ni–Fe–Mn/Cr systems

We have developed a procedure for x-ray fluorescence determination of the constituent composition and thickness of two-layer Ni–Fe–Mn/Cr films deposited on Polikor, an aluminum oxide ceramic. We have calculated correction coefficients taking into account interelement interference effects in this system. We have experimentally determined the density of the materials making up the composition of the films. We have established and present the metrological characteristics of the procedure developed.     

Studying the properties of Fe and Fe–Co nanotubes in polymer ion-track membranes

Iron and iron–cobalt nanostructures are probed by means of Mössbauer spectroscopy combined with scanning electron microscopy, energy-dispersion analysis, and X-ray diffraction. The obtained nanostructures are single-phase Fe_{1 ? x}Co _x (0 ≤ x ≤ 1) nanotubes that have high degrees of polycrystallinity and a bcc lattice 12 μm long and 110 ± 3 nm in diameter, with walls 21 ± 2 nm thick. A random distribution of the orientations of the magnetic momenta of Fe atoms are observed for Fe nanotubes, while Fe–Co nanotubes are characterized by a magnetic texture along their axes.     

Austenite layer and precipitation in high Co–Ni maraging steel

In high Co–Ni maraging steel, austenite has a great effect on the fracture toughness of the steel and the precipitated carbides are the main strengthening phase. In this study, both austenite layers and precipitation were observed and their formation theory was analyzed by Thermo-Calc simulation and several reported results. TEM and HRTEM observation results showed that the thickness of the austenite layers was about 5–10 nm and the length of the needle-like precipitated carbides was less than 10 nm. The carbides maintained coherent or semi-coherent relation with the matrix.     

Ternary compounds and isothermal section in Lu–Fe–Ga ternary system at 773 K

The isothermal section of the Lu–Fe–Ga ternary system at 773?K was investigated and constructed based on X-ray powder diffraction analysis. Thirteen binary compounds, Lu₂Fe₁₇, Lu₆Fe₂₃, LuFe₂, LuGa₃, LuGa₂, Lu₃Ga₅, LuGa, Lu₃Ga₂, Lu₅Ga₃, Fe₃Ga, Fe₆Ga₅, Fe₃Ga₄, FeGa₃, nine ternary solid solutions, T₁-LuFe_2–1.43Ga_0–0.57, T₂-LuFe_1.34–0.92Ga_0.68–1.08, T₃-LuFe_0.52–0.26Ga_1.48–1.74, T₅-LuFe_2.04–1.72Ga_0.96–1.28, T₆-Lu₆Fe_23–21.4Ga_0–1.6, T₇-Lu₂Fe_17–14.5Ga_0–3.5, T₈-Lu₂Fe_12.9–8.1Ga_4.1–8.9, T₉-LuFe_6.8–5.5Ga_5.2–6.5, T₁₀-LuFe_5.2–4.5Ga_6.8–7.5, and two ternary compounds, T₄-LuFe_2.35Ga_0.65 and T₁₁-Lu₂FeGa₈ have been confirmed. The structures of the five new ternary compounds or solid solution T₂, T₃, T₄, T₅ and T₈ are determined by Rietveld refinement method.     

Interdiffusion in lithium–lead melts

Interdiffusion in lithium-lead melts containing 10.0, 15.0, 18.1, 20.0, 25.1, 30.2, 38.2, 40.1, 43.1, 46.7, 50.2, 60.2, and 70.0 at. % Pb was investigated using gamma-ray attenuation technique in the temperature range from 720 to 1030 K. It has been found that the concentration dependence of the interdiffusion coefficient has a maximum in the vicinity of 20 at. % Pb. This phenomenon is shown to relate to a tendency of formation of short-range order in liquid alloys of lithium?lead.     

Anomalous Electrical Conductivity and Magnetization in Fe–Cr–Ni Austenite–Martensite Alloys

Technical Physics - We have measured the temperature dependence of the resistivity and magnetization of a special steel of the Fe–Cr–Ni austenite–martensite class in a wide...     

The ternary Ni–Al–Co embedded-atom-method potential for γ/γ Ni-based single-crystal superalloys: Construction and application

An Ni–Al–Co system embedded-atom-method potential is constructed for the γ(Ni)/γ(Ni3Al) superalloy based on experiments and first-principles calculations. The stacking fault energies(SFEs) of the Ni(Co, Al) random solid solutions are calculated as a function of the concentrations of Co and Al. The calculated SFEs decrease with increasing concentrations of Co and Al, which is consistent with the experimental results. The embedding energy term in the present potential has an important influence on the SFEs of the random solid solutions. The cross-slip processes of a screw dislocation in homogenous Ni(Co) solid solutions are simulated using the present potential and the nudged elastic band method. The cross-slip activation energies increase with increasing Co concentration, which implies that the creep resistance of γ(Ni)may be improved by the addition of Co.