Measurement of the density and surface tension of Ni-based superalloys in the liquid and mushy states

The densities of three Ni-based superalloys have been measured in both liquid and mushy states by both a modified sessile drop method (MSDM) and a modified pycnometric method (MPM) for alloys CMSX-4 and CM186LC, and for CMSX-10 alloy by MSDM only. The surface tensions of liquid CMSX-4, CM186LC, and CMSX-10 superalloys were measured using the sessile drop method. All measurements were carried out in a highly purified argon atmosphere with the oxygen partial pressure of less than 10⁻¹⁹ MPa in the gas outlet. The densities of all superalloys in both liquid and mushy states were found to decrease with increasing temperature. The volume thermal expansion of each superalloy in the mushy state was found to be higher than that in the liquid state. The densities determined by different methods have been critically assessed and recommended values in both liquid and mushy states are given as a linear function of temperature for the three Ni-based superalloys. The surface tension of liquid CMSX-4 superalloy was found to decrease with increasing temperature, while that of liquid CMSX-10 superalloy increases with increasing temperature. The wetting behavior of liquid CM186LC on the alumina substrate was found (1) to differ significantly from that of CMSX-4 and CMSX-10 and (2) to vary with time. A HfO₂-rich layer was found in the contact area of CM186LC with the alumina substrate, which could lead to some uncertainty in the value obtained for the surface tension determined for CM186LC.     

Heat storage in eutectic alloys

Classical thermodynamic equations based on the regular solution approximation yield enthalpic changes for eutectic transformation that agree roughly with values measured for several binary and ternary alloy systems by differential scanning calorimetry or differential thermal analysis. Restricting measurements to binary and ternary alloys of the relatively plentiful elements Al, Cu, Mg, Si and Zn, it has been verified that the best heat storage densities on a mass or volume basis are obtained with alloys rich in Si or Al, elements that have large heats of fusion. Several of these alloys have the highest heat-storage density reported for phase change materials that transform between 780 and 850 K. The Mg₂Si-Si eutectic, which has outstanding storage density at 1219 K, illustrates the utility of ordered intermetallic phases with large heat of formation that dissolve in the eutectic liquid to contribute to the entropy change.     

The effect of γ′ content on the densities of Ni-based superalloys

The γ′ phase increases the mechanical strength of Ni-based superalloys. Equations have been derived to calculate the atomic percent of γ′ phase from the Al content of the alloy. It is shown that increased γ′ phase content results in an increase in density (of the solid) and a decrease in the thermal expansion coefficient. Equations based on the Al content of the alloy have been derived to calculate the magnitude of these effects. The coarsening of the γ′ phase from 800 °C to 1000 °C was found to be accompanied by an increase in the temperature dependence of the thermal expansion coefficient. Densities for the entire temperature range of the solid alloys calculated with the equations are within 2 pct of measured values. The strong bonding between the Ni and Al was maintained in the liquid and resulted in increased densities. Equations were derived to quantify the effect on density (of the liquid) and the calculated density values for Ni-based superalloys were within 2 pct of the measured values. These uncertainties are commensurate with the experimental uncertainty in the measurements.     

Study on Diffusion of Hydrogen in AB_5 Non-Stoichiometric Hydrogen Absorbing Alloys

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Study on Diffusion of Hydrogen in AB5 Non－Stoichiometric Hydrogen Absorbing Alloys

The diffusion coefficient of hydrogen atoms in the studied alloys was electrochemically measured by chronoamperometry when the metallic hydride microelectrodes were completely discharged. It is found that the diffusion coefficient of hydrogen atoms decreases when cobalt is substituted for a minority of nickel. On the contrary, the diffusion eoefficient increases with the partial substitution of manganese or aluminum for nickel, which is related to the lattice constant and cell volumes of hydrogen absorbing alloys. The lattice constant c is obviously affected by the substitute elements greatly. The result shows that the expansion of cell volume resulted from the increase of value c causes the increase of diffusion coefficient which is especially obvious when the lattice constant is relatively low. However, this relationship is not clear if the lattice constant increases to some extent. It is suggested that this phenomenon is related to the interaction of hydrogen atoms with metallic atoms.     

Experimental study and modeling of the thermodynamic properties of Cu-Fe-Ni melts

The partial mixing enthalpy of nickel in ternary liquid Cu-Fe-Ni alloys is studied at 1873 K along sections characterized by ratios x _Cu: x _Fe = 3, 1, and 1/3 at x _Ni = 0–0.55. The investigations are undertaken using a high-temperature isoperibolic calorimeter. The temperature and composition dependence of the excess mixing Gibbs energy of liquid Cu-Fe-Ni alloys are described in terms of the Muggianu-Redlich-Kister model using the data obtained, the literature data on the activities of liquid alloy components, and the thermodynamic properties of melts of the boundary binary systems. This model is used to calculate isotherms of the thermodynamic properties of the liquid alloys over the entire composition range. The contribution of a ternary interaction to the integral mixing enthalpy of liquid Cu-Fe-Ni alloys is found to be mainly positive.     

Densities of Liquid K–Pb Alloys by a Dilatometric Method

Abstract

The densities and molar volumes of the liquid K–Pb alloys are measured from pure lead to X _Pb = 0.3433 using a dilatometric technique. The temperature range for the liquid alloys is generally 200 K above the liquidus temperature. The results indicate that the volume contraction reaches a maximum of 25% with respect to the ideal molar volume.

Résumé

Les densités et les volumes molaires d'alliages liquides K–Pb ont été mesurés pour des concentrations en plomb allant de 100% à X _Pb = 0.3433, au moyen d'une technique dilatométrique. L'intervalle de température des alliages liquides était généralement 200 K au dessus de la température du liquidus. Les résultats montrent que la contraction volumique atteint un maximum de 25% comparativement au volume molaire idéal.     

Density of Liquid Steel over Temperature Range of 1 803-1 873 K

The density of three kinds of liquid steel was measured by a modified sessile drop method over the temperature range of 1 803-1 873 K. It is found that the density of liquid steels decreases with increasing temperature and carbon content in steel. Both of the density and its absolute temperature coefficient of studied steels are smaller than the literature values of pure iron. The molar volume of the steels increases with increasing temperature.     

Density and viscosity of liquid Pu-U alloys

Density and viscosity determinations of liquid Pu-U alloys were made for five compositions, 5.5, 10.8, 16.6, 22.4, and 28.5 wt pct U, from near their liquidus temperatures to above 800°C. A vacuum pycnometric technique was used for the density determinations and an oscillating cup viscometer for the viscosity determinations. The partial molar volume of uranium was decreased approximately 15 pct in solutions containing up to 10.8 wt pct U and approached the normal molar volume at higher uranium concentration. The partial molar volume of plutonium changed by only 1 pct over the entire composition range. The viscosity of the alloys up to 10.8 pct U increased more rapidly than predicted from the pure components. Formerly with Monsanto Research Corp.     

The density and surface tension of dilute liquid Na-In alloys and comparison with liquid Na-Cd alloys

The density and surface tension of five liquid Na-ln alloys, containing between 0.5 and 7 at. pct In, have been measured in the temperature range 170° to 400°C using a maximum bubble pressure technique which incorporates an automatic pressure measuring and recording device. The results are compared with corresponding data reported previously for Na-Cd alloys. The gram-atomic volumes of the Na-ln alloys, calculated from the densities, indicate a substantial contraction on alloying which is, on average, about double that for the Na-Cd alloys and qualitatively consistent with thermodynamic data for the two systems. The surface tension of liquid sodium is increased slightly on adding indium, indicating a lower indium concentration in the surface than in the bulk, in contrast to the marked surface active behavior of cadmium. The surface excess concentrations of indium and cadmium are calculated using Gibbs’ adsorption equation. The surface excess entropy, estimated from the temperature dependence of the surface tension, is compared and briefly discussed for the two systems.     

A Thermodynamic Approach to a Density Model for Oxide Melts

In an attempt to estimate the densities of complex slags, a model based on the thermodynamics of slags developed earlier by the present authors is extended to ternary and multi‐component systems in the present work. The molar volumes of ternary and higher order systems were derived from the relative integral molar enthalpies of mixing of the corresponding slags. The higher order of slag systems has been predicted by using the parameters from the related binary sub‐systems, which have been evaluated earlier. Comparisons of calculated results with experimental data on molar volumes available in literature show a satisfying agreement for a number of systems, within the limits of experimental uncertainties. The model presents a promising method to compute the molar volume of slag systems where no experimental data is available using the abundance of thermodynamic data available. The model would also enable the generation of density data for slags containing Al₂O₃, CaO, FeO, MgO, MnO, and SiO₂ compatible with the corresponding thermodynamic data.     

Modeling solid solution strengthening in nickel alloys

The yield stress of multicomponent nickel solid solution alloys has not been modeled in the past with respect to the effects of composition and temperature. There have been investigations of the effect on the yield stress of solutes in binary systems at a fixed temperature, but the effects on the yield stress of multiple solute elements and temperature changes have not been investigated. In this article, two different forms of the trough model are considered for nickel-base alloys to determine the most applicable model for solid solution strengthening in the system. The yield stresses of three binary nickel-chromium and three ternary nickel alloys were determined at a range of temperatures. The yield stress of the alloys was then modeled using the Feltham equation. The constants determined in fitting the Feltham equation to the experimental data were then applied to other experimental solid solution alloys and also to published information on commercial solid solution nickel alloys. It was found that the yield stress of the nickel solid solution alloys could be modeled successfully using the Feltham equation.     

Predicting the liquidus temperature of complex nickel alloys

The production of steel and alloys ends with the casting of metal in a mold. In casting an alloy, its liquidus temperature must be known. This is especially important in developing a smelting technology for nickel alloys with a large number of alloying elements. In the present work, a model is developed for predicting the liquidus temperature of complex nickel alloys. The regression coefficients of the equations describing the liquidus and solidus lines of binary systems are determined on the basis of literature data regarding the phase diagrams of binary nickel systems with different elements. With increase in the set of data regarding the regression coefficients from 21 to 27 elements, a broad spectrum of complex nickel alloys may be covered. When the model based on data for binary alloys is tested for experimental liquidus temperatures of complex nickel alloys, the conclusion is that the model permits the prediction of the liquidus temperature of such alloys with sufficient precision for practical purposes (±19.8°C).     

Surface tension and wettability studies of liquid Fe-Ni-O alloys

Surface tensions of iron-nickel alloys were measured as a function of oxygen potential at 1550 °C using the sessile drop technique. The surface tension of pure liquid nickel and iron-nickel alloys was measured at a total pressure of 1 atmosphere under varying CO₂/CO ratios. An increase in the oxygen potential in the gas phase was found to correspond to a decrease in surface tension of pure nickel and iron-nickel alloys, indicating that oxygen is surface active in both liquid nickel and iron-nickel alloys. At low oxygen potentials, nickel additions to liquid iron were found to cause small decreases in alloy surface tensions; however, at higher oxygen potentials, the surface tension of the alloy exhibited a minimum value as nickel was added to iron. The adsorption coefficients of oxygen in liquid iron-nickel alloys and pure liquid nickel were determined from the surface-tension data using Belton’s analysis, and were found to be similar to those calculated from kinetic studies. Wettability of iron-nickel alloys on an alumina substrate was studied through contact-angle measurements. At a constant alloy nickel content, the contact angle between the alloy and alumina decreased with increased oxygen potential in the gas phase.     

A mathematical model describing carburization in multielement alloy systems

Previously, a finite difference model was set up describing the diffusion of carbon in high-temperature model alloys and its chemical reaction with one of the alloy components. The model described the formation of up to three different chromium carbides, two of which could coexist. This paper describes the further development of the model for application to commercial alloys. The model was extended to enable treatment of an arbitrary number of (a) metallic carbide-forming components in the alloys, (b) carbides which may form, (c) components out of which each carbide may be composed, and (d) carbides which may coexist. With this model, carbon concentration profiles and distribution profiles of precipitated carbides occurring during carburization of binary, ternary, and quaternary Ni-based alloys were calculated. Kinetic and thermodynamic data needed for the calculations were obtained by combining literacture data with experimental results and by fitting measured with calculated concentration profiles. The resulting calculated carbon profiles and carbide distributions were in good agreement with the experimental results. R. Supchulten, formerly with Kernforschungsanlage Jülich     

Thermodynamic study of liquid Cu-Mg alloys by vapor pressure measurements

Thermodynamic properties of liquid Cu-Mg alloys have been determined by magnesium vapor pressure measurements over pure liquid magnesium and liquid Cu-Mg alloys, in the composition range of 11 to 90 mole pct Mg between 845 and 1345 K, employing the transpiration technique. Based on the quadratic formalism suggested by Turkdogen and Darken for binary systems, analytical expressions have been derived representing integral and partial molar thermodynamic properties as functions of composition for the two terminal regions of suN Mg = 0 to 0.33 and 0.6 to 1.0. From the measured activity values of magnesium and copper, in the liquid alloys in equilibrium with solid intermetallic compounds, standard free energies of formation of Cu₂Mg(s) and CuMg₂(s) relative to pure solid components have been calculated and expressed as functions of temperature. Extractive Metallurgy Section, Metallurgy Division     

Densities of molten nickel mattes

The densities of molten nickel mattes Cu₂S-Ni₃S₂ and FeS-Ni₃S₂ were measured in the temperature interval 970° to 1321°C over the complete composition range. Several density values were also obtained for the ternary matte Cu₂S-FeS-Ni₃S₂ in the same temperature range. The densities of the binary mattes Cu₂S-Ni₃S₂, FeS-Ni₃S₂ and ternary matte Cu₂S-FeS-Ni₃S₂ were measured as 4.94 to 5.83 g per cu cm, 3.55 to 6.23 g per cu cm, and 2.65 to 4.92 g per cu cm, respectively. Molar volumes and excess molar volumes of the binary mattes were evaluated.     

Application of Nanocrystalline LaNi5-type Hydrogen Absorbing Alloys in Ni-MHx Batteries

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Estimation of Molar Volumes of some Binary Slags from Enthalpies of Mixing

In an effort to interlink the thermo chemical and thermo physical properties of slags, the present work was undertaken to derive the molar volumes of complex slags from the enthalpies of mixing of the corresponding slags. As a first step, binary systems of the following oxides were investigated; Al₂O₃, CaO, FeO, MgO, MnO, and SiO₂. An empirical correlation was derived between the enthalpies of mixing and molar volumes. A comparison of the computed results on the basis of the above relationship with the experimental data on molar volumes available in literature shows that the agreement between the calculated results and measured densities is satisfactory in the case of most of the binary systems, within the limits of experimentally uncertainties. The advantage of the present approach is that it would enable prediction of molar volumes of slags that are compatible with the thermodynamic data available.