Ni Melts Research Articles

Viscosity of Cu–Ni Melts

The kinematic viscosity of Cu–Ni melts with nickel contents of 10, 20, 30, 40, 50, 60, 70, 80, and 90 at % is measured. Kinematic viscosity is measured using the damped torsional vibrations of a crucible with a melt in the mode of sample cooling. The measuring results are discussed within the theory of absolute reaction rates. The temperatures at which the viscous flow characteristics (and thus the structural state of the melt) change are determined by analyzing the temperature dependences of kinematic viscosity. The patterns of the liquid–liquid transition in metal alloys of the Cu–Ni system that form a continuous series of solid solutions during crystallization are analyzed.

Density measurement of Ti–X (X = Cu, Ni) melts and thermodynamic correlations

The densities of Ti–X (X = Cu, Ni) melts were measured by a combination of electromagnetic levitation and a static magnetic field. The static magnetic field suppressed surface oscillation of the levitated sample droplet, which enhances the accuracy and precision of density measurements. Densities of the Ti–X melts varied linearly over a wide temperature range including a supercooled temperature region. The excess volumes of Ti–X were slightly negative over the entire composition range. These results are discussed within a thermodynamic framework considering the relationship between excess volume and thermodynamic properties such as excess Gibbs energy and enthalpy of mixing. The excess volume correlated more strongly with excess Gibbs energy for various binary alloy systems than with the enthalpy of mixing.

Size distribution of pores in metal melts at non-equilibrium cavitation and further stretching, and similarity with the spall fracture of solids

Non-equilibrium cavitation in liquids is similar in many aspects to the spall fracture of solids. The dynamics of cavitation and further evolution of melt with cavities are determined by the processes of nucleation and size variation in the ensemble of pores. Exploration of the statistical distribution of the pore sizes and its evolution in the course of the melt stretching is important for in-deep understanding of the spall fracture of melts and formulation of adequate models. Size distributions of pores in pure Al, Ni, Cu, Ti and Fe melts under stretching with ultra-high strain rates are investigated with the help of molecular dynamics simulations and analysis of the obtained atomic configurations by an algorithm of pore searching. The size distribution of pores fits well to exponential one at the stage of active homogeneous nucleation of pores in all considered cases. This form of distribution is explained by the exponential growth of the nucleation rate together with the decrease in the size of critical pores at the decrease in pressure. A transition from the exponential distribution to normal one in the course of stretching is found out for melts of most metals except Fe at the strain rates above 30/ns. The transition to the normal distribution is explained by depopulation in the area of small pores due to their collapse in conditions of the increase in pressure. The transition occurs near the pore number maximum, because the reaching the maximum indicates that the collapse becomes predominant over the nucleation. The collapse of small pores is accompanied by enlargement of the largest pores and rapid widening of the size distribution with increase in the mean pore size. This is a mediated mechanism of the volume redistribution from the small pores to the largest ones; this mechanism is the most pronounced in Al melt and the most suppressed in Fe melt. In most cases, it is accompanied by direct merging of pores that is, vice versa, the most active in Fe and the most delayed in Al. The merging knocks out pores from the distribution depending on both the pore size and the mutual position of pores; therefore, predominant depopulation of the area of small pores does not happens at merging. The prevalence of merging over the collapse in Fe melt at the strain rates above 30/ns prevents the transition to the normal distribution in this melt, and the size distribution remains exponential after the stopping of nucleation. The merging also leads to corruption of the size distribution at the late stages of stretching for all melts. Time evolution of the distribution parameters reflects the distribution widening and shows the beginning of the distribution corruption. It is shown for the case of Al melt that the general behavior of the size distribution of pores remains the same within the range of strain rates from 100/ns down to 1/ns. In the case of Fe melt, the transition to the normal size distribution arises for the strain rates below 10/ns because of the delaying of merging. Additional simulations for solid Ni and Al at room temperature show that the statistical behavior of the pore ensemble in solid metals at high-rate stretching is very similar to that is observed in the case of metal melts.

THERMODYNAMICS OF OXYGEN SOLUTIONS IN BORON-CONTAINING Fe – Ni MELTS

Fe – Ni alloys are widely used in modern technology. Boron is one of the alloying components in these alloys. Oxygen is one of the harmful impurities in Fe – Ni alloys, it presents in the metal in dissolved form or in the form of oxide nonmetallic inclusions. The presence of oxygen in these alloys degrades their service properties. The study of thermodynamics of the oxygen solution in boron-containing Fe – Ni melts is of considerable interest for the practice of such alloys production. Thermodynamic analysis of oxygen solutions in boroncontaining Fe – Ni melts has been carried out. The equilibrium constant of interaction of boron and oxygen dissolved in the Fe – Ni melts, the activity coefficients at infinite dilution, and the interaction parameters characterizing these solutions were determined for melts of different composition. In the interaction of boron with oxygen in Fe – Ni melts, the oxide phase, in addition to B2 O3 , contains FeO and NiO. Values of the mole fractions of B2 O3 , FeO and NiO in the oxide phase for different boron concentrations in Fe – Ni melts were calculated at 1873 K. In the case of an iron melt at low boron contents, the mole fraction of boron oxide is ~0.1. As the content of nickel and boron increases in the melts, the mole fraction of boron oxide in the oxide phase increases and, in the case of pure nickel, is close to unity. Dependences of the oxygen solubility on the contents of nickel and boron in the studied melts were calculated. With increasing nickel content in melt deoxidation ability of chromium increases significantly. The oxygen solubility curves in boron-containing Fe – Ni melts pass through a minimum whose position shifts to the higher boron content with an increase in the nickel content in melt. Boron contents in minimum points on the oxygen solubility curves and the corresponding minimum oxygen concentrations were determined.

Thermodynamics of Oxygen Solution in Fe–Ni Melts Containing Boron

Fe–Ni alloys are widely used in engineering today. They are sometimes alloyed with boron. Oxygen is a harmful impurity in Fe–Ni alloys. It may be present in dissolved form or as nonmetallic inclusions. The presence of oxygen in Fe–Ni alloys impairs their performance. Research on the thermodynamics of oxygen solutions in Fe–Ni melts containing boron is of considerable interest in order to improve alloy production. The present work offers a thermodynamic analysis of solutions of oxygen in Fe–Ni melts containing boron. The equilibrium constant of the reaction between boron and oxygen dissolved in the melt in such systems is determined. The activity coefficients at infinite dilution and the interaction parameters in melts of different composition are also calculated. When boron reacts with oxygen in Fe–Ni melts, the oxide phase contains not only B2O3 but also FeO and NiO. The mole fractions of B2O3, FeO, and NiO in the oxide phase are calculated for different boron concentrations in Fe–Ni melts at 1873 K. For iron melts with low boron content, the mole fraction of boron oxide is ~0.1. With increase in the nickel and boron content in the melts, the boron-oxide content in the oxide phase increases. Its mole fraction is close to one for pure nickel. The solubility of oxygen in Fe–Ni melts is calculated as a function of the nickel and boron content. The deoxidizing ability of the boron improve significantly with increase in nickel content in the melt. The curves of oxygen solubility in Fe‒Ni melts containing boron pass through a minimum, which is shifted to higher boron content with increase in nickel content in the melt. The boron content at the minima on the curves of oxygen solubility are determined, as well as the corresponding minimum oxygen concentrations.

On the glass transition of the one-component metallic melts

In this paper, the conditions for one-component metallic melts vitrification by quenching from a liquid state were formulated. It is shown that the tendency to the glass formation drastically increases with the temperature of melting. The maximum glass layer thickness and the associated cooling rates along with the vitrification temperatures was determined for Al, Cu, and Ni melts deposited on the Cu substrate. The results are in agreement with the available experimental data. Based on analytical solution of the impinging droplet solidification, the numerical value of the early-introduced asymptotic Ω criterion, which separates equilibrium and non-equilibrium phase transitions, was determined. Good agreement between the calculated and experimental values of the thickness of the splats shows that Ω criterion indeed predicts a priori a scenario of solidification.

Constant electrical resistivity of Ni along the melting boundary up to 9 GPa

AbstractCharacterization of transport properties of liquid Ni at high pressures has important geophysical implications for terrestrial planetary interiors, because Ni is a close electronic analogue of Fe and it is also integral to Earth's core. We report measurements of the electrical resistivity of solid and liquid Ni at pressures 3–9 GPa using a 3000 t multianvil large volume press. A four‐wire method, in conjunction with a rapid acquisition meter and polarity switch, was used to overcome experimental challenges such as melt containment and maintaining sample geometry and to mitigate the extreme reactivity/solubility of liquid Ni with most thermocouple and electrode materials. Thermal conductivity is calculated using the Wiedemann‐Franz law. Electrical resistivity of solid Ni exhibits the expected P dependence and is consistent with earlier experimental values. Within experimental uncertainties, our results indicate that resistivity of liquid Ni remains invariant along the P‐dependent melting boundary, which is in disagreement with earlier prediction for liquid transition metals. The potential reasons for such behavior are examined qualitatively through the impact of P‐independent local short‐range ordering on electron mean free path and the possibility of constant Fermi surface at the onset of Ni melting. Correlation among metals obeying the Kadowaki‐Woods ratio and the group of late transition metals with unfilled d‐electron band displaying anomalously shallow melting curves suggests that on the melting boundary, Fe may exhibit the same resistivity behavior as Ni. This could have important implications for the heat flow in the Earth's core.

Normal spectral emissivity and heat capacity at constant pressure of Fe–Ni melts

The normal spectral emissivity at 807 nm and molar heat capacity at constant pressure of Fe–Ni melts were successfully measured by the combination of an electromagnetic levitation technique and a static magnetic field. The static magnetic field suppressed the surface oscillation and translational motion of the levitated sample droplet to reduce the experimental uncertainty in the measurements. For all compositions of the melts, the normal spectral emissivity values and molar heat capacities showed negligible temperature dependence. The excess heat capacity of the melts was evaluated as a function of composition. This analysis showed a positive deviation from the Neumann–Kopp rule over the entire composition range. Moreover, enthalpy of mixing was calculated from the excess heat capacity up to 2200 K.

Evaporation of reaction-zone components in the low-temperature plasma treatment of chromium-bearing melts

The evaporation of iron, Fe–Cr, Fe–Ni, and Fe–Cr–Ni melts at the plasma spot in treatment by low-temperature argon plasma is studied. Experiments with different masses of metal and with variation in arc power of the plasmatron are conducted so as to determine the conditions corresponding to stable surface temperature of the metal. The results show that, for experiments in which the plasma flux completely exposes the surface of the metal droplet, arc power no less than 2.0 kW is optimal; the mass of the metal should be 5‒10 g. The evaporation process is studied as function of the melt composition, and the evaporation rates are determined. Of the alloys considered, Fe–Cr–Ni melt is characterized by the highest evaporation rate in the neutral atmosphere of a laboratory plasma furnace. The surface temperature of the melt is determined indirectly, on the basis of the evaporation rate. The surface temperature of the plasma-treated melt is found to vary in the range 1950–2100 K with variation in arc power from 1.6 to 2.4 kW.

Densities of Fe–Ni melts and thermodynamic correlations

The densities of liquid Fe–Ni alloys were measured accurately by combination of an electromagnetic levitation technique and a static magnetic field. The static magnetic field suppressed the surface oscillation of the levitated sample droplet, which reduced the experimental uncertainty in the density measurement. Densities were determined over a wide temperature range and included a supercooled region. The densities of all Fe–Ni alloys investigated vary linearly with temperature over the range of measurements. The excess volumes were slightly positive over the entire composition range. The results were discussed within a thermodynamic framework using relationship between excess volume and thermodynamic properties such as excess Gibbs energy and enthalpy of mixing. The excess volume is correlated positively with excess Gibbs energy and enthalpy of mixing for various binary alloy systems.

The dynamics of femtosecond pulsed laser removal of 20 nm Ni films from an interface

The dynamics of femtosecond laser removal of 20 nm Ni films on glass substrates was studied using time-resolved pump-probe microscopy. 20 nm thin films exhibit removal at two distinct threshold fluences, removal of the top 7 nm of Ni above 0.14 J/cm2, and removal of the entire 20 nm film above 0.36 J/cm2. Previous work shows the top 7 nm is removed through liquid spallation, after irradiation the Ni melts and rapidly expands leading to tensile stress and cavitation within the Ni film. This work shows that above 0.36 J/cm2 the 20 nm film is removed in two distinct layers, 7 nm and 13 nm thick. The top 7 nm layer reaches a speed 500% faster than the bottom 13 nm layer at the same absorbed fluence, 500–2000 m/s and 300–700 m/s in the fluence ranges studied. Significantly different velocities for the top 7 nm layer and bottom 13 nm layer indicate removal from an interface occurs by a different physical mechanism. The method of measuring film displacement from the development of Newton's rings was refined so i...

Continuum model of tensile fracture of metal melts and its application to a problem of high-current electron irradiation of metals

A continuum model of the metal melt fracture is formulated on the basis of the continuum mechanics and theory of metastable liquid. A character of temperature and strain rate dependences of the tensile strength that is predicted by the continuum model is verified, and parameters of the model are fitted with the use of the results of the molecular dynamics simulations for ultra-high strain rates (≥1–10/ns). A comparison with experimental data from literature is also presented for Al and Ni melts. Using the continuum model, the dynamic tensile strength of initially uniform melts of Al, Cu, Ni, Fe, Ti, and Pb within a wide range of strain rates (from 1–10/ms to 100/ns) and temperatures (from melting temperature up to 70–80% of critical temperature) is calculated. The model is applied to numerical investigation of a problem of the high-current electron irradiation of Al, Cu, and Fe targets.

Short-range structural signature of transport properties of Al–Ni melts

Ab initio molecular dynamics simulations are performed to investigate dynamic properties of Al–Ni melts. Along the T=1795K isotherm, we show that self-diffusion coefficients and the viscosity exhibit a strong non-linear dependence as a function of composition. We further demonstrate that this behavior has an underlying origin in the composition-dependent local structural ordering characterized by a strong interplay between icosahedral short-range order and chemical short-range order in the Ni-rich composition range. Finally we evidence that this structural evolution is at the origin of the breakdown of the Stokes–Einstein relation.

OXYGEN SOLUBILITY IN A NIOBIUM-CONTAINING Fe – Ni MELTS

The oxygen solubility in the niobium-containing ironnickel melts has been experimentally studied at 1823 K using the Fe – 40 % Ni alloy as an example. It was shown that niobium decreases the oxygen solubility in this melt. The equilibrium constant of interaction of niobium and oxygen dissolved in the Fe – 40 % Ni melt (lgK(1) (Fe – 40 % Ni) = –4.619), the Gibbs energy of this reaction ( = 161,210 J/mol), and the interaction parameters characterizing these solutions ( = –0.630; = –0.105; = 0.010) were determined. The equilibrium constant of interaction of niobium and oxygen dissolved in the Fe – Ni melts, the Gibbs energy of reaction of niobium and oxygen interaction, and the interaction parameterscharacterizing these solutions were calculated in a wide range of concentrations at 1823 K. Oxygen solubility in the various compositions niobium-containing Fe – Ni melts was determined at 1823 K. With an increase of the nickel content in melt the affinity of niobium to oxygen increases substantially. This is due to the fact that, when the nickel content in melt increases, the bond strengths of oxygen with the melt base weakens

The melting curve of Ni to 1 Mbar

The melting curve of Ni has been determined to 125 GPa using laser-heated diamond anvil cell (LH-DAC) experiments in which two melting criteria were used: firstly, the appearance of liquid diffuse scattering (LDS) during in situ X-ray diffraction (XRD) and secondly, plateaux in temperature vs. laser power functions in both in situ and off-line experiments. Our new melting curve, defined by a Simon–Glatzel fit to the data where TM(K)=[(PM18.78±10.20+1)]1/2.42±0.66×1726, is in good agreement with the majority of the theoretical studies on Ni melting and matches closely the available shock wave melting data. It is however dramatically steeper than the previous off-line LH-DAC studies in which determination of melting was based on the visual observation of motion aided by the laser speckle method. We estimate the melting point (TM) of Ni at the inner-core boundary (ICB) pressure of 330 GPa to be TM=5800±700 K(2σ), within error of the value for Fe of TM=6230±500 K determined in a recent in situ LH-DAC study by similar methods to those employed here. This similarity suggests that the alloying of 5–10 wt.% Ni with the Fe-rich core alloy is unlikely to have any significant effect on the temperature of the ICB, though this is dependent on the details of the topology of the Fe–Ni binary phase diagram at core pressures. Our melting temperature for Ni at 330 GPa is ∼2500 K higher than that found in previous experimental studies employing the laser speckle method. We find that those earlier melting curves coincide with the onset of rapid sub-solidus recrystallization, suggesting that visual observations of motion may have misinterpreted dynamic recrystallization as convective motion of a melt. This finding has significant implications for our understanding of the high-pressure melting behaviour of a number of other transition metals.

Viscosity and diffusivity in melts: from unary to multicomponent systems

Viscosity and diffusivity, two important transport coefficients, are systematically investigated from unary melt to binary to multicomponent melts in the present work. By coupling with Kaptay’s viscosity equation of pure liquid metals and effective radii of diffusion species, the Sutherland equation is modified by taking the size effect into account, and further derived into an Arrhenius formula for the convenient usage. Its reliability for predicting self-diffusivity and impurity diffusivity in unary liquids is then validated by comparing the calculated self-diffusivities and impurity diffusivities in liquid Al- and Fe-based alloys with the experimental and the assessed data. Moreover, the Kozlov model was chosen among various viscosity models as the most reliable one to reproduce the experimental viscosities in binary and multicomponent melts. Based on the reliable viscosities calculated from the Kozlov model, the modified Sutherland equation is utilized to predict the tracer diffusivities in binary and multicomponent melts, and validated in Al–Cu, Al–Ni and Al–Ce–Ni melts. Comprehensive comparisons between the calculated results and the literature data indicate that the experimental tracer diffusivities and the theoretical ones can be well reproduced by the present calculations. In addition, the vacancy-wind factor in binary liquid Al–Ni alloys with the increasing temperature is also discussed. What’s more, the calculated inter-diffusivities in liquid Al–Cu, Al–Ni and Al–Ag–Cu alloys are also in excellent agreement with the measured and theoretical data. Comparisons between the simulated concentration profiles and the measured ones in Al–Cu, Al–Ce–Ni and Al–Ag–Cu melts are further used to validate the present calculation method.

Strength and Reliability of High Temperature Transient Liquid Phase Sintered Joints

Low-temperature transient liquid phase sintering (LT-TLPS) can be used to form high-temperature joints between metallic interfaces at low process temperatures. In this paper, we will describe the processing and shear strength, along with the shock fatigue resistance of sintered joints made by this process. Joints made from different ratios of Ni and Cu high melting temperature constituents paired with Sn-based low melting temperature constituents have been evaluated. For the shear studies, the softening behavior of test samples joined by Ni-Sn3.5Ag and (Ni,Cu)-Sn3.5Ag sinter pastes have been assessed using a fixture designed for high temperature shear testing up to 600°C. The reliability of sinter paste joints in drop-shock environments will be discussed. It is shown that joints formed from these sinter pastes possess improved drop-shock reliability compared to Sn3.5Ag solder joints and melting temperatures considerably higher than those of conventional high temperature solders (e.g. Pb5.0Sn2.5Ag).

Diffusivities and atomic mobilities in the Al–Ce–Ni melts

The recently developed Arrhenius formula of modified Sutherland equation was applied to calculate the self- and impurity diffusivities in liquid Al, Ce and Ni. Based on the measured tracer and chemical diffusivities available in the literature together with the reliable thermodynamic parameters of the liquid phase in the Al–Ce–Ni system and the atomic mobilities of binary Al–Ni melts, the atomic mobilities in Al–Ce–Ni melts were evaluated using the DICTRA (diffusion-controlled transformations) software package. Comprehensive comparisons between the calculated results and the experimentally measured data show that most of the diffusivities from different sources can be well reproduced by the atomic mobilities obtained in the present work. The atomic mobilities were further verified by comparing the model-predicted concentration profiles and the measured ones in two liquid Al–Ce–Ni diffusion couples.

Viscosity of Al–Ni and Al–Co melts in the Al-rich area

The temperature and concentration dependencies of viscosity (v) of liquid alloys of binary Al–Ni and Al–Co systems, with the Al content of more than 90 at.% have been studied (from here on the alloying element concentration is given in at.%). It has been found that the viscosity polytherms of the melts containing 2.7% to 5% of Ni and 0.01% to 1.5% of Co deviate from the Arrhenius dependence. The non-monotonic dependencies of viscosity and the energy of viscous flow activation of the Al–Ni melts and the liquid Al–Co melts in the vicinity of the liquidus line on the alloying element concentration have been obtained.

On the formation of Al3Ni2 intermetallic compound by aluminothermic reduction of nickel oxide

Simultaneous reduction of NiO and formation of Al 3 Ni 2 intermetallic compound at 880, 940 and 1000 °C were investigated by means of the thermal reduction method. The optimal Ni contents for the starting samples were determined at different times and temperatures through the compositional analysis. The microstructure of the metallic quenched samples was observed by scanning electron microscope. Moreover, the X-ray diffraction analysis and energy disperse spectrometry were applied to characterize the formation of the phases. The results showed that the metallic samples consisted of Al 3 Ni 2 , Al 3 Ni and Al phases and that there was no trace of Ni, NiO and Al 2 O 3 . It was found that after 10 min at the applied temperatures, the reaction completed. For the longer time, the dispersed Al 3 Ni 2 nuclei were grown and its continuous network formed. By increasing the temperature, the thickness of the Al 3 Ni precipitation around Al 3 Ni 2 phase is enhanced in the samples with the same Ni content. A model was proposed for these reactions. ► Simultaneous reduction of NiO, and Al 3 Ni 2 intermetallics formation at temperatures lower than Ni melting point. ► Presently a mechanism for such a process. ► Parametric study of microstructure and formed phases.