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.     

Thermochemical properties of ternary Si-Ni-Al liquid alloys

Partial (for aluminum) and integral mixing enthalpies of ternary Si-Ni-Al liquid alloys are examined by high-temperature calorimetry under isoperibolic conditions at 1770 ± 5 K. Alloys of five radial sections with a constant ratio of silicon-to-nickel mole fractions (x_Si/x_Ni = 0.85/0.15; 0.7/0.3; 0.5/0.5; 0.3/0.7, and 0.15/0.85) within the interval compositions to aluminum mole fraction x_Al ∼ 0.6 are studied. The mixing enthalpies of Si-Ni-Al alloys are characterized by great exothermal values. Exothermal partial enthalpies of aluminum mixing increase at infinite dilution with increasing nickel concentration in starting binary alloys ( reaches −17.0 ± 3.3 kJ/mole for section with x_Si/x_Ni = 0.85/0.15 and −119.0 ± 11.2 kJ/mole for x_Si/x_Ni = 0.15/0.85). An analysis of alloy-formation energy parameters in the ternary Si-Ni-Al system indicates that the interaction of the components in the bounded binary Si-Ni and Ni-Al systems greatly contributes to Δ_mH, the effect of the former prevailing. The thermochemical properties of ternary alloys and of Ge-Ni-Al melts and simulated mixing enthalpies of ternary Sn (C)-Ni-Al liquid alloys are compared. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 3–4 (454), pp. 79–85, 2007.     

Thermodynamics of Liquid Alloys and Metastable Phase Transformations in the Copper - Titanium System

We have used solution calorimetry at temperatures of 1573 K and 1873 K over broad concentration ranges to study the mixing enthalpy of Cu - Ti liquid alloys. The molar mixing enthalpies of the system are significant negative values. We have established the temperature dependence of the molar mixing enthalpies of the system: there is an increase in their exothermicity as the temperature is lowered. The significant negative mixing enthalpies of the system allow us to conclude that the chemical bonds are localized in the studied melts and consequently associates form. We tested this conclusion within ideal associated solution theory, which describes well the results obtained with a set of CuTi and CuTi₂ associates. Using the model obtained, we have calculated the excess thermodynamic functions of mixing (enthalpy, Gibbs free energy, heat capacity) for the liquid alloys. We estimated the Gibbs energies of fcc, bcc, and hcp solutions in the system by the CALPHAD method, using data from the initial sections of the phase diagrams and from the corresponding thermodynamic data. We have calculated the metastable phase equilibria between the limiting solid solutions and the liquid or supercooled liquid phase. It was shown that for the supercooled liquid and the amorphous phase, a broad concentration range of relative thermodynamic stability can be obtained. The concentration range of amorphization of Cu - Ti melts corresponds to the position of the metastable liquidus line and the T₀ line at temperatures close to the temperature range of amorphous solidification. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 67–80, May–June, 2005.     

Thermodynamic Properties and Phase Equilibria of Nd–Ni Alloys

Isoperibolic calorimetry has been used for the first time to determine the mixing enthalpies of binary Nd–Ni liquid alloys in the range 0 < xNi < 0.5 at 1733 K and range 0.55< xNi < 1 at 1773 K. The binary Nd–Ni melts are characterized by significant negative mixing enthalpies with a minimum of –33.9 ± 0.8 kJ/mole at xNi = 0.63 and 1750 K. In the temperature range studied (1733–1773 K), the mixing enthalpies of the melts are described by polynomial ΔH = xNi (1 – xNi )× × (–75.32 – 103.41 xNi + 273.45$$ {x}_{Ni}^2 $$ – 817.02$$ {x}_{Ni}^3 $$ +548.58$$ {x}_{Ni}^4 $$). The ideal associated solution (IAS) model was used to calculate the activities of components, molar fractions of associates, Gibbs energies, and mixing entropies using our ΔH and $$ \varDelta \overline{H}i $$ and literature data on the formation enthalpy of nickelides and the Nd–Ni phase diagram. All intermediate phases were considered stoichiometric, with zero excess heat capacity. Five associates were selected for the calculation: Nd2Ni, NdNi, NdNi2, NdNi3, and NdNi5. Most of them agree in composition with the intermetallides in this system. Only one of them does not exist in solid state. This is associate Nd2Ni, whose composition is close to that of the Nd7Ni3 intermetallide. The activities of the Nd–Ni melt components show high negative deviations from ideal solutions. Associates of simplest composition, NdNi and NdNi2, are predominant in the melts. The mixing entropies of Nd–Ni liquid alloys are negative (minimum value is close to –6.4 J/mole · K). All our thermodynamic properties indicate that there is strong energy of interaction between Ni and Nd. The liquidus curves of the Nd–Ni system were calculated using the IAS model parameters.     

Thermochemistry of alloys of transition metals: Part III. Copper-Silver, -Titanium,Zirconium, and -Hafnium at 1373 K

The enthalpies of mixing of liquid copper with liquid silver and with solid titanium, zirconium, and hafnium have been measured by high temperature reaction calorimetry at 1371 to 1373 K. A least squares treatment of the data for copper-silver alloys yields the following expression for the molar enthalpy of mixing: ΔH_mix = ϰ_Agϰ_Cu(17.66 − 5.46 ϰ_Ag) kJ mol⁻¹. The enthalpies of solution of solid titanium, zirconium, and hafnium in dilute solutions in liquid copper are all exothermic; the following values were found: -2.0 kJ mol⁻¹ for Ti, -52.5 kJ mol⁻¹ for Zr, and -46.3 kJ mol⁻¹ for Hf. These values are all significantly less exothermic than predicted by the semiempirical theory of Miedema. The enthalpies of formation of congruent melting intermetallic phases in the systems Cu-Ti, Cu-Zr, and Cu-Hf were measured by drop calorimetry or by solution calorimetry in liquid copper. The enthalpies of formation of the solid alloys have been compared with corresponding data for the liquid alloys.     

Calorimetric study and description of the composition dependence of the mixing enthalpy of liquid Cu—Fe—Co aloys

The partial enthalpy of cobalt in ternary liquid Cu-Fe-Co alloys is studied at a temperature of 1873 K along sections characterized by ratios x _Cu/x _Fe = 3, 1, and 1/3 in the composition range x _Co = 0–0.55. The experiments have been carried out on a high-temperature isoperibolic calorimeter. The composition dependences of the partial mixing enthalpy of the cobalt and the integral mixing enthalpy of Cu-Fe-Co melts are described using the Muggianu-Redlich-Kister equation over the entire concentration triangle. The contributions of a ternary interaction to the partial mixing enthalpy of cobalt and the integral mixing enthalpy of Cu-Fe-Co melts are calculated.     

Calorimetric research on the heat of formation of liquid alloys of copper with group IIIA and group IVA metals

Using a high-temperature isoperibolic calorimeter of our own design we have determined the concentration dependences of the enthalpy of mixing for alloys of copper with scandium, yttrium, lanthanum, titanium, zirconium, and hafnium. The directly measured enthalpies of dissolution of solid group IVA metals in liquid copper are converted into partial molar enthalpies of mixing, taking into account the data on the high-temperature component of the enthalpies and the enthalpies of fusion of the pure components. The enthalpies of mixing of the liquid alloys are given in tables and equations. The thermodynamic properties are interpreted within the framework of the theory of an ideal associative solution. Donbass State Academy of Machine-Building, Kramatorsk. Translated from Poroshkovaya Metallurgiya, Nos. 5/6(395), pp. 25–36, May–June, 1997.     

Thermochemistry of binary alloys of lanthanum with 3d-transition metals

The enthalpy of mixing for liquid binary alloys of lanthanum with 3d-transition metals (Sc, Ti, V, Cr, and Fe) is determined by a calorimetric method within the field of compositions rich in lanthanum. Data for the partial enthalpy of mixing in the La-3d-metal system with infinite dilution demonstrates a complex relationship of a change in it in the series of 3d-metals connected with gradual filling of the 3d-zone due to alloy formation with lanthanum. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 65–71, May–June, 2006.     

Enthalpies of formation of liquid binary (copper + iron, cobalt, and nickel) alloys

The enthalpies of formation of liquid binary (Cu+Fe, Co, Ni) alloys are studied by direct reaction calorimetry in the whole range of compositions at 1873, 1823, and 1753 K, respectively. The integral molar enthalpies of mixing are found to be positive in all three systems with the maximum values approaching 10.8±0.7 kJ/mol⁻¹ at x _Fe=0.43, 7.1±0.9 kJ/mol⁻¹ at x _Co=0.55, and 3.7±0.5 kJ/mol⁻¹ at x _N1=0.53. Partial molar enthalpies at infinite dilution constitute 59.4±3.3 kJ/mol⁻¹ for iron, 44.3±4.1 kJ/mol⁻¹ for cobalt, and 14.9±2.2 kJ/mol⁻¹ for nickel in liquid copper. Similar values for copper in liquid iron, cobalt, and nickel are 36.6±3.9, 45.3±6.0, and 17.7±4.4 kJ/mol⁻¹, respectively. The results are compared with the thermodynamic data available in literature and discussed in connection to the equilibrium-phase diagrams. In particular, decreasing from Cu-Fe to Cu-Ni liquid alloys positive values of the excess thermodynamic functions of mixing are fully in accord with the growing stability of phases in these systems. The excess entropies of mixing are estimated by combining the established enthalpies with carefully selected literature data for the excess Gibbs functions. Analysis of possible contributions to the enthalpies of mixing indicates that the experimentally established regularity in ΔH values along the 3d series is likely to arise from the difference in d-band width and d-electron binding energy of the alloy constituents.     

Development of RuAl-based cast alloys

Heterophase RuAl-based alloys with a β-RuAl + (1–20) vol % ɛ-Ru structure and alloyed with chromium, titanium, and hafnium are produced by vacuum arc melting. The effect of the method of preparing charge materials on their behavior during alloy formation is studied. The effect of a structure on the deformability of the alloys at room temperature is estimated. All alloys exhibit ductility and can be deformed by upsetting at a strain higher than 10–12%. The effect of deformation by upsetting at 800°C and subsequent heat treatment on the structure and properties of the alloys is investigated. The high-temperature strengths of RuAl-, TiAl-, Ni₃Al-, and NiAl-based alloys are compared by measuring their hot hardnesses at temperatures up to 1100°C. The high-temperature strength characteristics of the RuAl-based alloys are higher than those of the Ni3Al-, TiAl-, and NiAl-based alloys over the entire temperature range under study; at temperatures ≥900°C, the hardness of ruthenium monoaluminide is higher than those of the other alloys by a factor of 2–4.     

Thermodynamics of component interactions in Ge−Fe−Al liquid alloys

Partial enthalpies of mixing of aluminum in Ge−Fe−Al alloys along various radial sections in the ternary system with constant x_Ge/x_Fe ratio were determined with the aid of a high-temperature isoperibolic calorimeter. Integral heats of mixing were calculated from the partial heats for aluminum using Darken method. It was determined that alloy formation in the ternary system is accompanied by small exothermic heat effects. Component interactions in the binary Ge−Fe and Fe−Al systems have a marked effect on the thermodynamics of alloy formation in the ternary system. Taras Shevchenko National University, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8(408), pp. 68–74, July–August, 1999.     

Free energies of mixing in the liquid iron-cobalt orthosilicates at 1450°c

Measurements have been made of the equilibrium between liquid iron-cobalt orthosilicates and solid iron-cobalt alloys. It is shown that the integral free energies of mixing of the oxide components and the integral and partial molar free energies of mixing of the pseudobinary (orthosilicate) components can be derived from a knowledge of the metallic activities in such exchange equilibria. The thermodynamic properties are presented for 1450°C. It is found that the integral free energy of mixing shows a maximum deviation of −2.1 (±0.3) kJ per mole of MO • 1/2 SiO₂ from ideal silicate mixing.     

Thermodynamic studies on the Mg-Ga system

By means of concentration cells of the following type: Mg(s) |MgCl₂ in (LiCl-KCl)_eut (1) |Mg-Ga (1) the partial thermodynamic data of Mg in Mg-Ga liquid solutions have been obtained in the composition range 0. l≤x_Mg≤0.7 and at temperatures from 760 to 900 K. In addition, the enthalpies of mixing of liquid Gallium with liquid Magnesium have been measured calorimetrically at 973 K. The experimental values for the enthalpies of mixing from emf and calorimetric measurements are in good agreement. These values are compared with thermodynamic data reported in the literature and used for the calculation of thermodynamic data of intermetallic compounds existing in the Mg-Ga-system. Additionally, the heat of formation of Mg₅Ga₂ has been determined by solution calorimetry. The thermodynamic data of the liquid alloys can be described by an association model, and these results explain the possibility to obtain glassy metals by rapid cooling of these melts.     

Structures at Glassy,Supercooled Liquid,and Liquid States in La-Based Bulk Metallic Glasses

Local atomic structures at glassy, supercooled liquid, and liquid states for La-based bulk metallic glasses (BMGs) have been investigated by in-situ high-temperature X-ray diffraction. It is found that the coordination number of about 15.1 ± 0.1 for the La₆₂Al₁₄Cu_11.7Ag_2.3Ni₅Co₅ alloy does not depend on temperature up to liquid temperature, while it decreases slightly with temperature for the La₆₂Al₁₄Cu₂₄ and La₆₂Al₁₄Cu₂₀Ag₄ alloys. The S(q) data recorded at the supercooled liquid region can be well described by the Debye theory. For the three alloys, the volume expansion coefficient and the slopes of radii variation for the first to third nearest neighboring coordination shells show differences at glassy-to-supercooled liquid transition, while no obvious changes were detected at supercooled liquid-to-liquid transition for them. The linear expansion coefficient value (β = 1.6 ± 0.1 × 10^–5 K^–1) below the glass transition temperature deduced from S(q) data is consistent with that detected by the dilatometer (β = 1.25 × 10^–5 K^–1) for the La₆₂Al₁₄Cu_11.7Ag_2.3Ni₅Co₅ BMG.     

Electrochemical Formation of Mg–Li–Sm Alloys by Codeposition from LiCl–KCl–MgCl2–SmCl3 Molten Salts

In this article, the electrochemical method of preparing Mg–Li–Sm alloys by codeposition in LiCl–KCl–MgCl₂–SmCl₃ melts was investigated. Transient electrochemical techniques, such as cyclic voltammetry, chronopotentiometry, and chronoamperometry were used to explore the electrochemical formation of Mg–Li–Sm alloys. Chronopotentiograms demonstrated that the codepositon of Mg, Li, and Sm occurred when current densities were more negative than −0.31 A cm⁻². Chronoamperograms indicated that the onset potential for the codeposition of Mg, Li, and Sm was −2.40 V, and the codeposition of Mg, Li, and Sm was formed when the applied potentials were more negative than −2.40 V. The different phases of Mg–Li–Sm alloys were prepared by galvanostatic electrolysis and characterized by X–ray diffraction (XRD), optical microscope (OM), and scanning electron microscopy (SEM). An inductively coupled plasma (ICP) analysis showed that the lithium and samarium contents in Mg–Li–Sm alloys could be controlled by the concentrations of MgCl₂ and SmCl₃. The results demonstrated that Sm could refine the grains dramatically. When the Sm content was 0.8 wt pct, the grain size was the finest.     

Estimation of complex concentration in a regular associated solution

Novel procedures have been developed to estimate the concentration ofA _pB –type clusters in liquid alloys with the aid of regular associated solution model utilizing activity coefficients of the components at infinite dilution and activity data at any one other composition. The equilibrium constant for the dissociation of clusters as well as the nature and magnitude of pairwise interaction energies between unassociated atoms and clusters have been evaluated without making any assumptions whatsoever. These enable estimation of thermodynamic properties of the liquid alloys at any other desired composition. The utility of the procedures has been demonstrated with respect to the thermodynamics of association in molten Mg-Sn and In-Sb alloys. The calculated activities, enthalpies and free energies are shown to be in excellent agreement with experimental values.     

Influence of rare-earth metals on the high-temperature strength of Ni<Subscript>3</Subscript>Al-based alloys

The influence of the content of reaction- and surface-active alloying elements (rare-earth metals (REMs)) and the method of their introduction into cast high-temperature γ′-Ni₃Al-based intermetallic alloys, which are thermally stable natural eutectic composites, on their structure-phase state and the mechanical properties is studied. The life of low-alloy heterophase γ′ + γ cast high-temperature light Ni₃Al-based alloys is shown can be increased at temperatures exceeding 0.8T _m (T _m is the melting temperature of Ni3Al) due to additional stabilization of the single-crystal structure of these alloys with submicron and nanometer-sized particles of the phases formed by refractory and active REMs. It is also shown that stage-by-stage fractional introduction of all components into alloys during vacuum induction melting with allowance for their reaction activities (most refractory metals are introduced in the form of low-melting-point master alloys at the first stage of vacuum induction melting, and lanthanum is introduced with a master alloy in the optimal contents of 0.1–2 wt % into the charge of VKNA-1V and VKNA-25 alloys at the final stage) leads to the formation of a modified structure stabilized by nanoprecipitates of nickel and aluminum lanthanides and the phases formed by refractory metals. This method increases the life of VKNV-1V-type alloys (0.5 wt % Re) at 1000–1200°C by a factor of ∼1.7 and that of VKNA-25-type alloys (1.2 wt % Re and Co) by a factor of ∼3.     

Plastic deformation and fracture of binary TiAl-base alloys

The mechanical behavior of binary TiAl alloys containing 46 to 60 at. pct Al has been studied in bulk materials preparedvia rapid solidification processing. Bending and tensile tests were carried out at room temperature as a function of Al concentration. A few alloys were also tested from liquid nitrogen temperature to ∼ 1000°C. Deformation substructures were studied by analytical transmission electron microscopy and fracture modes by scanning electron microscopy (SEM). It was found that both microstructure and composition strongly affect the mechanical behavior of TiAl-base alloys. A duplex structure, which contains both primary y grains and transformedγ/α ₂ lamellar grains, is more deformable than a single-phase or a fully transformed structure. The highest plasticities are observed in duplex alloys containing 48–50 at. pct Al after heat treatment in the center of theγ + α phase field. The deformation of these duplex alloys is facilitated by 1/2[110] slip and {111} twinning, but very limited superdislocation slip occurs. The twin deformation is suggested to result from a lowered stacking fault energy due to oxygen depletion or an intrinsic change in chemical bonding. Other factors, such as grain size and grain boundary chemistry and structure, are important from a fracture point of view. The results on the deformation and fracture modes as a function of test temperature are also discussed.     

Rate of nitrogen desorption from liquid iron-carbon and iron-chromium alloys with argon

The rate of nitrogen desorption from inductively stirred liquid iron, iron-carbon, and iron-chromium alloys with argon carrier gas has been measured by the sampling method for a wide range of nitrogen, carbon, and chromium contents mainly at 1600 °C. The results obtained by the present work and other data of previous investigators are used to clarify the reaction mechanism of nitrogen desorption from liquid iron. The rate of nitrogen desorption from liquid iron and iron alloys is second order with respect to nitrogen content in the metal under the present condition, and mutual relationships among interfacial chemical reaction, liquid-phase mass transfer, and gas-phase mass transfer are elucidated. The effects of oxygen and sulfur on the rate of nitrogen desorption are given byk _' ^{c ’} = 3.15ƒ_N ² [1/(1 + 300a₀ + 130a_s)]. Carbon dissolved in iron increases the rate of nitrogen desorption, and chromium decreases it. The effects of these alloying elements can be explained by the change of the nitrogen activity in the metal. This paper is based on a presentation made at the G. R. Fitterer Symposium on Nitrogen in Metals and Alloys held at the 114th annual AIME meeting in New York, February 24–28, 1985, under the auspices of the ASM-MSD Thermodynamic Activity Committee.