Thermodynamic Properties of Si - Mn - Y System Alloys

High-temperature isoperibolic calorimetry has been used to measure the partial enthalpies of mixing for yttrium in the Si - Mn - Y ternary system at 1775 K along sections with various atomic ratios of silicon to manganese (0.85/0.15; 0.7/0.3; 0.6/0.4; 0.5/0.5; 0.3/0.7) for yttrium concentrations in the range 0 < x_Y < 0.4 together with the partial molar enthalpies of manganese for x_Si/x_Y = 0.8/0.2. The integral enthalpies of mixing have been calculated from the partial ones for yttrium by Darken’s method. The addition of yttrium to the Si - M binary system to give the ternary Si - Mn - Y system increases the exothermic effects of the alloying substantially. There is a substantial effect on the thermodynamic parameters of the ternary alloys from the atomic interactions in the Si - Y and Si - Mn binary systems.__________Translated from Poroshkovaya Metallurgiya, Nos. 3–4(442), pp. 64–69, March–April, 2005.     

Enthalpies of Solution and Mixing for Graphite in Molten Silicon at 2000 K

Partial and integral enthalpies of mixing have been determined in an isoperibolic calorimeter for liquid alloys in the silicon – carbon binary system at 2000 K. These enthalpies of mixing are small exothermic quantities which agree with published data. The enthalpy of mixing _f Hº₂₉₈ has been calculated for silicon carbide.     

Interactions in Molten Aluminum (Silicon) ― Boron Alloys

Isoperibolic calorimetry has been used to determine the partial and integral enthalpies of mixing for liquid alloys in the binary systems aluminum (silicon) boron at 1873 K. Those enthalpies are small exothermic quantities, which agree with published data. The enthalpies of mixing have also been calculated from the _f H ₂₉₈ of the metal borides. The concentration dependence has been determined for these enthalpies in binary alloys in the nontransition metal boron systems.     

Enthalpies of formation of liquid (copper + manganese) alloys

The enthalpies of formation of liquid (Cu + Mn) alloys were measured in the isoperibolic heat-flux calorimeter at 1573 K in the entire range of compositions. The integral molar enthalpy of mixing was found to be negative in the range of molar fractions 0 < x _Mn < 0.31, with ΔH(min) = −0.69 ± 0.27 kJ mol⁻¹ at x _Mn = 0.12, and positive in the range 0.31 < x _Mn < 1, with ΔH(max) = 3.67 ± 0.36 kJ mol⁻¹ at x _Mn = 0.75. Limiting partial molar enthalpies of manganese and copper were calculated as = −18.0 ± 6.6 kJ mol⁻¹ and = 29.1 ± 4.9 kJ mol⁻¹, respectively. The results are discussed in comparison with the thermodynamic data available in the literature and the equilibrium phase diagram.     

Thermal chemistry and short-range order in Co-Sb melts

The enthalpies of mixing for the liquid Co-Sb alloys are measured by isoperibolic calorimetry at 1600 K over the whole concentration range relative to liquid Sb and undercooled liquid Co. The minimal integral enthalpy of mixing is −6.3 ± 0.6 kJ/ mole at x_Co = 0.50. Activity of components, Gibbs energy, and the entropy of mixing are calculated using a short-range ordering model considering CoSb associates formed in molten Co-Sb alloys. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 5–6 (455), pp. 96–101, 2007.     

Enthalpy of mixing of liquid Cu-Ti-Zr alloys

The enthalpy of mixing of liquid Cu-Ti-Zr ternary alloys is studied by high-temperature isoperibolic calorimetry at 1873 K along three ray sections characterized by the ratios x _Zr: x _Cu = 3: 7, x _Ti: x _Cu = 3: 7, and x _Zr: x _Ti = 1 at x _Cu = 1?0.4. The isotherm of the integral enthalpy of mixing of these melts is described in terms of the Redlich-Kister-Muggianu model. Along with the substantial contributions of binary copper-titanium and copper-zirconium interactions, the contribution of a ternary interaction to the enthalpy of mixing of liquid Cu-Ti-Zr alloys also exists. The first partial enthalpies of mixing of Ni, Al, Si, Sn, and Y with the melts are studied to determine the character of the interaction between the ternary Cu-Ti-Zr melts and metal additions that facilitate amorphization upon melt quenching. The introduction of these metals into the ternary melts is shown to increase their thermodynamic stability.     

The high-temperature creep behavior of nickel-rich Ni-W solid solutions

The steady-state creep behavior of four nickel-rich Ni-W solid solutions (1, 2, 4, and 6 wt pct W) was investigated in the temperature range 850° to 1050°C. Constant stress tensile creep tests were performed in vacuum in the stress range 3000 to 7000 psi. Activation energies for creep were observed to be 71.4 ± 2.0, 74.4 ± 3.0, and 75.8 ±2.0 kcal per mole, after correcting temperature dependence of the elastic modulus, for alloys containing 2,4, and 6 pct W respectively. These values closely approximate the activation energies for the weighted diffusion coefficient, =D _Ni D _W/(X _W D _Ni) whereX _Ni andX _w are the atom fractions of nickel and tungsten respectively, andD _Ni andD _w are the diffusion coefficients of nickel and tungsten in the alloy. The steady-state creep rates exhibit a power law stress dependence with an exponent,n, equal to 4.8 ±0.2 for all of the alloys studied. For tests conducted at temperatures and stresses such that both the diffusivity, , and the ratio of the applied stress to the elastic modulus, σ/E, are. held constant, the steady-state creep rate, , was found to vary with the stacking fault energy, γ, according to the empirical relation ∼ γ^{4 2±4} over the range of creep rates studied. W. R. Johnson, formerly Graduate Student, Stanford Univeristy, Stanford, Calif.     

Enthalpy of mixing of liquid Ni-Zr and Cu-Ni-Zr alloys

The partial (Δ and the integral (ΔH) enthalpies of mixing of liquid Ni-Zr and Cu-Ni-Zr alloys have been determined by high-temperature isoperibolic calorimetry at 1565 ± 5 K. The heat capacity (C _p) of liquid Ni₂₆Zr₇₄ has been measured by adiabatic calorimetry (C _p=53.5±2.2 J mol⁻¹ K⁻¹ at 1261±15 K). The integral enthalpy of mixing changes with composition from a small positive (Cu-Ni, ΔH (x _Ni=0.50, T=1473 to 1750 K)=2.9 kJ mol⁻¹) to a moderate negative (Cu-Zr; ΔH(x _Zr=0.46, T=1485 K)=−16.2 kJ mol⁻¹) and a high negative value (Ni-Zr; ΔH(x _Zr=0.37, T=1565 K)=−45.8 kJ mol⁻¹). Regression analysis of new data, together with the literature data for liquid Ni-Zr alloys, results in the following relationships in kJ mol⁻¹ (standard states: Cu (1), Ni (1), and Zr (1)):for Ni-Zr (1281≤T≤2270 K),

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.     

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.     

EMF and calorimetric measurements on the Mg-In liquid solutions

By means of concentration cells: Mg (s)IMgClM₂ (LiCl)KCl)_eut(l)|Mg-In(l) partial molar thermodynamic data of Mg in Mg-ln liquid alloys have been determined in the composition range 0.03 ≤X _Mg ≤ 0.6 and at temperatures 770 to 890 K. Integral molar enthalpies measured in a Calvet calorimeter at 948 and 1008 K were used for calculation of the partial molar enthalpy of magnesium, . Values of with partial molar free energies of Mg from emf studies were used for derivation of partial molar excess entropies.     

Enthalpy of mixing for melts of Ge-Ga-Gd and Si-Ga-Gd ternary systems

We have determined the partial mixing enthalpies in Ge(Si)-Ga-Gd ternary systems by high-temperature calorimetric measurements. We computed the integral mixing enthalpies from H _Gd using the Darken method. We have shown that alloy formation in these systems is accompanied by large exothermic effects. We have established that the interaction between components in binary Gd-Ge(Si) and Gd-Ga liquid alloys has a large influence on the thermodynamic behavior of these ternary systems.Taras Shevchenko National University. Translated from Poroshkovaya Metallurgiya, Nos. 7–8, pp. 84–88, July—August, 1996.     

Enthalpy of mixing of liquid Cu-Ni-Ti alloys at 1873 K

The enthalpy of formation of ternary Cu-Ni-Ti alloys at 1873 K is studied at x _Ti = 0?0.6 along sections characterized by fixed ratios: x _Ni: x _Cu = 1: 3, 1: 1, and 3: 1. For investigations, a high-temperature isoperibolic calorimeter is used. The isotherm of the integral enthalpy of mixing of liquid Cu-Ni-Ti alloys at 1873 K is described using the Redlich-Kister polynomials for binary systems and the Maggianu model for ternary interaction. The contribution of ternary interaction to the heat of formation of the alloys in the concentration range x _Ti < 0.45 is exothermic; in the other fields of the concentrational triangle, this contribution is endothermic. The first partial enthalpies of mixing of Al, Sn, Si, Y, Zr, Hf, or Fe with Cu-Ni-Ti melts are exothermic, which indicates an increase in the thermodynamic stability of the liquid phase as a result of the dissolution of additions of these metals.     

Diffusion studies in the β (B2), β′ (bcc), and γ (fcc) Fe-Ni-Al alloys at 1000 °C

Diffusion studies were carried out in the Fe-Ni-Al system at 1000 °C with solid-solid diffusion couples assembled with β (B₂), β′ (bcc), and γ (fcc) single-phase alloys for the development of diffusion structures, diffusion paths, and for the determination of interdiffusion and intrinsic diffusion coefficients. The diffusion structures were examined by optical and scanning electron microscopy, and the concentration profiles were determined by electron microprobe analysis. Diffusion couples included several series of β vs γ and β′ vs γ diffusion couples characterized by a common terminal alloy bonded to several terminal alloys with varying compositions. The development of planar and nonplanar interfaces, as well as two-phase layers, as observed in various couples, were related to the diffusion paths. The interdiffusion fluxes of individual components were calculated directly from the experimental concentration profiles, and the diffusional interactions among components were examined in the light of zero-flux planes (ZFPs) and flux reversals, which were identified in several couples. Ternary interdiffusion coefficients ( (i, j = Al, Ni)), with Fe considered as the dependent concentration variable, were evaluated at composition points of the intersection of diffusion paths of single-phase couples and of multiphase couples that developed planar interfaces. The interdiffusion coefficients were the largest in magnitude for the β′ alloys, especially near the β/β′ miscibility gap, and decreased for the β and γ alloys. In the β and γ phases, the main interdiffusion coefficient for Al was larger than those for Ni and Fe. Also, Fe interdiffused faster than Ni in the Fe-rich β and β′ phases. The cross-interdiffusion coefficients ( and ) were negative in all three phases. In general, the coefficients were larger in magnitude than the coefficients; however, the magnitude of was greater than that of near the β/(β + γ) phase boundary on the ternary isotherm. In the β phase, the magnitude of (i, j=Al, Ni) coefficients increased over 1 to 2 orders of magnitude with a decrease in the Al concentration and increase in the Fe/Ni concentration ratio. Interdiffusion coefficients, extrapolated from the ternary coefficients for binary alloys, were consistent with those in literature. Intrinsic diffusion coefficients were also determined at selected compositions. In addition, tracer diffusion coefficients were estimated for the binary Fe-Al and Ni-Al alloys at selected compositions, from an extrapolation of ternary interdiffusion coefficients.     

Thermochemical Properties of Liquid Alloys in Fe ― O and Fe ― O ― Metal Systems

An isoperibolic calorimeter has been used to determine the partial and integral enthalpies of mixing for liquid alloys in the binary Fe ― O system and ternary Fe ― O ― M ones at 1915 K. The enthalpies of mixing in these systems are high exothermic quantities, which agree with published data. It is found that the first partial enthalpy of mixing for oxygen is _280 kJ/mole. The enthalpies of mixing have been calculated from the standard enthalpies of formation Δ_f H ^º ₂₉₈ for iron oxides throughout the concentration range. The enthalpies of mixing have been calculated and measured for binary alloys in the Fe ― O system, which are correlated one with the other.     

Thermodynamics of Ca-Ga alloys

The enthalpies of formation of the intermetallic compounds CaGa₄, Ca₃Ga₈, and CaGa₂, at 298.15 K, were determined by high-temperature liquid gallium solution calorimetric measurements to be −24.9 ± 4.9 kJ·g at.⁻¹, −25.4 ± 2.4 kJ·g at.⁻¹, and −38.8 ± 4.8 kJ·g at.⁻¹, respectively. The enthalpies of formation of CaGa₄ at 988 K and that of Ca₃Ga₈ at 1070 K were determined, using precipitation calorimetry, to be −28.2 ± 1.7 kJ·g at.⁻¹ and −22.5 ± 1.4 kJ·g at.⁻¹, respectively. The integral enthalpy of mixing of the (Ca-Ga) liquid alloys (ΔH ⁰) measured at 1309 K are described by the following Redlich-Kister equation:

Thermodynamic activities and phase boundaries for the alloys of the Ni3Al-Ni3Ti pseudobinary section in the Ni-Al-Ti system

The pseudobinary section Ni₃Al-Ni₃Ti of the ternary Ni-Al-Ti system has been investigated by ther-mal analysis and Knudsen effusion mass spectrometry. The solidus of the pseudobinary section and the thermodynamic activities of Ni and Al have been determined in the alloys Ni_0.75A1_0.25-xTi_x of the compositionsx = 0.00 to 0.21. Moreover, the thermodynamic activities of Ni and Ti in Ni₃Ti (x = 0.25) as well as the Gibbs energy of mixing of the Ni_0.75Ti_0.25 phase resulted. The ionization cross-sectional ratio Σ(Ni)/Σ(Ti) = 0.77 has been evaluated for the electron impact energy of 50 eV.     

Assessment of service induced microstructural damage and its rejuvenation in turbine blades

Correlations between service induced microstructural degradation and creep properties in investment cast IN738LC turbine blades are discussed. Microstructural degradation in the form of γ’ coarsen-ing, MC carbide degeneration, formation of continuous networks of grain boundary M₂₃C₆ carbides, and the disappearance of serrated grain boundaries are considered in some detail. Their influence on primary (t _p ,ε _p ), secondary (t _s , ε _s ,ε _m ) and tertiary (t_t, ε_t) creep behavior is analyzed through rela-tionships of the form: