Experimental investigation and thermodynamic assessment of the Hf–Ge system

The Hf–Ge system has been studied via experiment, first-principles calculations and thermodynamic modeling. 15 annealed Hf–Ge alloys were analyzed by means of X-ray diffraction, scanning electron microscope with energy dispersive X-ray analysis, differential thermal analysis and high temperature reaction calorimetry. The major experimental results are as follows: (I) the heat contents of the Hf₃Ge and HfGe₂ phases were measured from 400 to 1050 °C; (II) the enthalpy of formation at 298 K for the HfGe₂ phase (?67 ± 4 kJ/mol atoms) was measured; (III) the invariant reaction temperature of Liquid ? (Ge) + HfGe₂ was determined to be at 932.6 ± 2.3 °C; and (IV) the previously reported phases HfGe and Hf₃Ge₂ were not found in the present experiment. In addition, the enthalpies of formation at 0 K for the Hf₃Ge, Hf₂Ge, Hf₅Ge₃, Hf₅Ge₄, Hf₃Ge₂, and HfGe₂ phases were computed from first-principles calculations in order to provide the necessary energy levels for the thermodynamic properties of the binary compounds. Based on the present experimental results and first-principles calculations as well as the reliable literature data, the Hf–Ge system was modeled by using a CALPHAD approach.     

Experimental investigation and thermodynamic calculation of the phase equilibria in the Cu–Mo–Ni ternary system

The phase equilibria at 900 °C, 1000 °C, 1100 °C, 1200 °C and 1300 °C in the Cu–Mo–Ni system were experimentally determined by means of optical microscopy (OM), electron probe microanalyzer (EPMA) and X-ray diffraction (XRD) on the equilibrated alloys. The experimental results firstly found that the fcc-type miscibility gap exists at 900 °C, 1000 °C, 1100 °C and 1200 °C in the Cu–Mo–Ni system, and the solubility of Cu in the MoNi phase at 900 °C, 1000 °C, 1100 °C and 1200 °C are about 0.5 at.%, 1.5 at.%, 1.7 at.% and 4.0 at.%, respectively. The as-cast Cu₂₀Mo₂₀Ni₆₀ (at.%), Cu₂₀Mo₃₀Ni₅₀ (at.%), Cu₁₀Mo₆₀Ni₃₀ (at.%), Cu₇₀Mo₁₀Ni₆₀ (at.%), Cu₂₀Mo₆₀Ni₂₀ (at.%) and Cu₈₀Mo₁₀Ni₁₀ (at.%) alloys appear the separated macroscopic morphologies, which are caused by the liquid phase separation on cooling, while the as-cast Cu₁₀Mo₂₅Ni₆₅ (at.%), Cu₃₂Mo₅Ni₆₃ (at.%) and Cu_30.7Mo_6.3Ni₆₃ (at.%) alloys show the homogenous microscopic morphologies. On the basis of the experimental data investigated by the present and previous works, the phase equilibria in the Cu–Mo–Ni system were thermodynamically assessed by using CALPHAD (Calculation of Phase Diagrams) method, and a consistent set of the thermodynamic parameters leading to reasonable agreement between the calculated results and experimental data was obtained.     

Experimental investigation and thermodynamic calculation of phase equilibria in the In–Sb–Zn ternary system

Binary thermodynamic data, successfully used for phase diagram calculations of binary systems In–Sb, In–Zn, and Sb–Zn, were used for prediction of phase equilibria in ternary In–Sb–Zn system. The liquidus projection, invariant equilibria and several vertical sections were calculated using the CALPHAD method. Alloys, situated along three calculated vertical sections, were investigated by differential thermal analysis (DTA). The experimentally determined phase transition temperatures were compared with predicted results. Phase identification of selected samples was done using scanning electron microscopy (SEM) with energy dispersive X-ray microanalysis (EDS).     

Experimental investigation and thermodynamic description of the Mg–Y–Zr system

The Mg–Y–Zr system was studied via experimental investigation and thermodynamic modeling. Four diffusion couples and four key alloys of the Mg–Y–Zr system at 500 °C were prepared. The phase relations of the Mg–Y–Zr system were investigated by means of X-ray diffraction, scanning electron microscopy, and electron probe microanalysis. No ternary compound was found at 500 °C. The solubility of (αZr) in the Mg–Y intermetallics, i.e., Mg₂₄Y₅, Mg₂Y and MgY, was determined to be negligible. The differential scanning calorimetry measurement was performed on the Mg–Y–Zr alloys to obtain the phase transition temperature. The present thermodynamic calculations of the Mg–Y–Zr system matched well with the experimental data. The presently established Mg–Y–Zr phase diagram can offer a better understanding of the recent processing technique of creep-resistant magnesium alloys.     

Experimental investigation and thermodynamic assessment of the Mg–Zn–Gd system focused on Mg-rich corner

The phase equilibria in the Mg-rich corner of Mg–Zn–Gd ternary system at 673 K were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) equipped with energy dispersive X-ray spectroscopy (EDS), and electron probe microanalysis (EPMA). Three ternary phases, X-(Mg₁₂ZnGd), W-(Mg₃Zn₃Gd₂) and I-(Mg₃Zn₆Gd₁), have been identified, which are in equilibrium with Mg solid solution. A thermodynamic modeling and optimization of Zn–Gd and Mg–Zn–Gd systems has been carried out for the first time using the CALPHAD method. The sublattice model was used to describe the thermodynamic functions of both solution phases and intermetallic phases presented in these systems. In particular, order/disorder transition between BCC_B2 and BCC_A2 has been taken into account, and their Gibbs energies were expressed with identical function. The thermodynamic database was applied to case studies of experimentally observed microstructures and demonstrated that it is a valuable basis for alloy design.     

Experimental investigation and thermodynamic calculation of the Ga–Sb–Zn phase diagram

Phase equilibrium of ternary Ga–Sb–Zn system was investigated by applying CALPHAD method and using literature thermodynamic data for constitutive binary systems. The liquidus surface and isothermal section at 673 K were calculated. Calculated results were verified experimentally on the alloys samples with the compositions corresponding to the characteristic vertical sections: SbZn (1:1)–Ga; GaZn(1:1)–Sb; and GaSb(1:1)–Zn. Phase transitions temperatures were determined by differential thermal analysis and differential scanning calorimetry. Microstructure and phase composition investigation were investigated by using scanning electronic microscopy with energy dispersive spectrometry. The experimental and analytical results showed good agreement, concerning the temperatures of phase transitions and phase compositions of alloys concerned.     

Experimental investigation and thermodynamic prediction of the Bi–Sb–Zn phase diagram

Phase diagram of the ternary Bi–Sb–Zn system was investigated experimentally by DTA and SEM-EDS methods and analytically by CALPHAD method. The liquidus projection, invariant equilibria, several vertical sections and isothermal section at 300 °C were predicted using COST 531 thermodynamic database. Phase transition temperatures of alloys along three predicted vertical sections of the Bi–Sb–Zn ternary system with molar ratio Bi:Sb = 1, Bi:Zn = 1 and Sb:Zn = 1, were measured by differential thermal analysis (DTA). Predicted isothermal section at 300 °C was compared with the results of the scanning electron microscope (SEM) with energy dispersive spectrometry (EDS) analysis from this work.     

Experimental investigation and thermodynamic calculation of Bi–Ga–Sb phase diagram

Abstract

Phase diagram of the Bi–Ga–Sb ternary system has been investigated by DTA and SEM with EDS measurements. Phase transition temperatures in four vertical sections and isothermal section at 500°C were studied. Experimental results were compared with calculated phase diagram by the Calphad method.     

Experimental determination and thermodynamic modeling of phase equilibria in the Cu–Cr system

Liquidus temperatures in the Cu–Cr system at compositions of 10.0–72.7 at.% Cr were determined using electromagnetic levitation melting. The present data agree with the prediction of a recent thermodynamic study of the system for compositions up to 20.0 at.% Cr. However, they show large and positive deviations for other compositions. Microscopic studies reveal that compositions between 10.0 and 50.5 at.% Cr solidified into a dendritic microstructure, whereas those between 55.9 and 72.7 at.% Cr solidified into a droplet-shaped microstructure. The microstructure of the latter type provides direct evidence for the existence of a stable miscibility gap over Cr-rich compositions. Phase equilibria in the Cu–Cr system were calculated using the CALPHAD method. A novel phase diagram was proposed for the Cu–Cr system, which shows a monotectic reaction between compositions of 50.8 and 83.2 at.% Cr at an invariant temperature of 2020 ± 22 K. The novel phase diagram has reduced the discrepancies between the literature data.     

Experimental investigation of phase equilibria in the Cu–Ni–Zr system

Phase equilibria in the Cu–Ni–Zr ternary system have been measured through alloy sampling combined with diffusion couple approach. According to the phase relations identified with electron probe microanalysis and X-ray diffraction techniques, isothermal sections at both 1073 and 1293 K were constructed. It is evident that remarkable ternary solubility occurs in almost all binary intermetallic phases at both temperatures. The formerly reported ternary compounds T1 (Cu_20–40Ni_40–60Zr₂₀) and T2 (Cu_20–25Ni_60–65Zr₁₅) were not verified in this work. No other ternary compound was detected. In addition, continuous dissolution between Cu₁₀Zr₇ and Ni₁₀Zr₇ at 1073 K was observed.     

Experimental study and thermodynamic modeling of the Al–Co–Cr–Ni system

Abstract

A thermodynamic database for the Al–Co–Cr–Ni system is built via the Calphad method by extrapolating re-assessed ternary subsystems. A minimum number of quaternary parameters are included, which are optimized using experimental phase equilibrium data obtained by electron probe micro-analysis and x-ray diffraction analysis of NiCoCrAlY alloys spanning a wide compositional range, after annealing at 900 °C, 1100 °C and 1200 °C, and water quenching. These temperatures are relevant to oxidation and corrosion resistant MCrAlY coatings, where M corresponds to some combination of nickel and cobalt. Comparisons of calculated and measured phase compositions show excellent agreement for the β–γ equilibrium, and good agreement for three-phase β–γ–σ and β–γ–α equilibria. An extensive comparison with existing Ni-base databases (TCNI6, TTNI8, NIST) is presented in terms of phase compositions.     

Experimental study and thermodynamic modeling of the Al–Co–Cr–Ni system

A thermodynamic database for the Al–Co–Cr–Ni system is built via the Calphad method by extrapolating re-assessed ternary subsystems. A minimum number of quaternary parameters are included, which are optimized using experimental phase equilibrium data obtained by electron probe micro-analysis and x-ray diffraction analysis of NiCoCrAlY alloys spanning a wide compositional range, after annealing at 900 °C, 1100 °C and 1200 °C, and water quenching. These temperatures are relevant to oxidation and corrosion resistant MCrAlY coatings, where M corresponds to some combination of nickel and cobalt. Comparisons of calculated and measured phase compositions show excellent agreement for the β–γ equilibrium, and good agreement for three-phase β–γ–σ and β–γ–α equilibria. An extensive comparison with existing Ni-base databases (TCNI6, TTNI8, NIST) is presented in terms of phase compositions.     

Structure and microwave dielectric properties of 5BaO–2V2O5 binary ceramic system

5BaO–2V₂O₅ ceramic has been prepared by conventional solid state reaction method. The X-ray diffraction and Laser Raman studies have been carried out to ascertain the phase purity and crystal structure of the prepared composition. The microwave dielectric properties of the well sintered ceramic compacts were measured by Hakki & Colemann post resonator and cavity perturbation techniques using a vector network analyzer. The 5BaO–2V₂O₅ ceramic exhibits a low dielectric constant of 12.1, relatively good quality factor of 26,790 GHz, and a small temperature variation of resonant frequency of 7 ppm/°C in the microwave frequency region.     

Experimental investigation of the stability of a clearance‐excited rotor system with optimal parameters

Abstract

The instability caused by aerodynamic forces from blade‐tip clearance is one of the most troublesome problems found in high performance tur‐bomachinery. An optimization technique has been proposed in previous work to improve the stability of a rotor‐bearing system. In this work, the validity and the practical procedure of the optimization technique are experimentally verified and demonstrated using a rotor‐bearing system. The experimental results verify the important theoretical conclusion that the threshold of stability of a rotor‐bearing system can be significantly increased by slight modification of the rotor diameters. Two examples are given to show the detailed procedure when the proposed optimization technique is used to increase the threshold of stability of an existing rotor‐bearing system.     

Density function theory investigation on the thermodynamic properties of the Li–N–H system

The electronic structures and formation enthalpies of compounds in the Li–N–H system have been studied by using the density functional theory. In order to evaluate the competition between each reaction in the system, the chemical potential phase diagrams of compounds in the Li–N–H system have been computed and discussed. Our calculations show that for LiNH₂, Li⁺ combines with [NH₂]^- by an ionic bond. For Li₂NH, the N–H bond displays covalent characteristics. The calculated formation enthalpy of compounds in the Li–N–H system is in agreement with previous results, the LiNH₂ is −212.27 kJ mol⁻¹, LiH is −91.66 kJ mol⁻¹, Li₂NH is −243.14 kJ mol⁻¹, Li₄NH is −309.72 kJ mol⁻¹, Li₃N is −189.11 kJ mol⁻¹, and NH₃ is −102.27 kJ mol⁻¹, respectively. Using the chemical potential phase diagrams, six reversible reactions are discussed. It is found that Li₄NH takes part in the three reversible reactions and some NH₃ formed in the system react with other compounds in the Li–N–H system. These reversible reactions are confirmed by the proposed mechanism from experiments.