Thermodynamic properties of the Al–Fe–Ni system acquired via a hybrid approach combining calorimetry,first-principles and CALPHAD

A reaction calorimeter coupled with first-principles calculations was employed to obtain enthalpies of formation for τ₁ (Al₉FeNi) and τ₂ (Al₁₀Fe₃Ni) compounds. The previous thermodynamic model for describing the disorder/order transition (fcc_A1/L1₂) in the Al–Fe–Ni system was modified to extrapolate this model to quaternary and higher-order systems. The first-principles energy calculations for the end-members of sub-lattice models in ternary compounds and L1₂ phase were performed to facilitate subsequent modeling. The existence of the experimentally observed miscibility gap for ternary B2-ordered phase is detected by the present calculation. Such a feature cannot be identified with available thermodynamic software due to the tiny difference between the Gibbs energies associated with different phase assemblages. A set of thermodynamic parameters for the Al–Fe–Ni system was obtained via thermodynamic modeling. Numerous experimental data including phase diagram, thermodynamic properties and site occupation of Fe in B2 phase are well accounted for by the present modeling.     

The Al-Er-Mg ternary system Part I: Experimental investigation

Investigation of phase equilibria in the ternary system Al-Er-Mg has been carried out by means of differential thermal analysis (DTA), powder x-ray diffraction (XRD), light optical microscopy (LOM), scanning electron microscopy (SEM), and quantitative electron probe microanalysis (EPMA). The isothermal section at 400 °C has been established. An extended homogeneity region with Al substitution for Mg at a constant Er content has been found for (Mg_1−x Al _x )Er (0≤x≤0.78); a few other boundary binary phases give lower ternary solubility. A ternary compound, τ, of Al_66.7Er₁₀Mg_23.3 stoichiometry, has been found to exist in the isothermal section at 400 °C.     

The Al-Er-Mg ternary system Part I: Experimental investigation

Investigation of phase equilibria in the ternary system Al-Er-Mg has been carried out by means of differential thermal analysis (DTA), powder x-ray diffraction (XRD), light optical microscopy (LOM), scanning electron microscopy (SEM), and quantitative electron probe microanalysis (EPMA). The isothermal section at 400 °C has been established. An extended homogeneity region with Al substitution for Mg at a constant Er content has been found for (Mg_1−x Al _x )Er (0≤x≤0.78); a few other boundary binary phases give lower ternary solubility. A ternary compound, τ, of Al_66.7Er₁₀Mg_23.3 stoichiometry, has been found to exist in the isothermal section at 400 °C.     

Enthalpy of Formation in the Al-Ni-Ti System

The Al-Ni-Ti ternary system forms the basis of several alloy systems of practical importance. This study was undertaken to provide additional experimental thermodynamic data for the modeling of the Al-Ni-Ti system. High-temperature direct reaction calorimetry has been used to determine the standard enthalpy of formation of several Al-Ni-Ti alloys. The stability of the L2₁ structure over the B2 structure at the stoichiometric composition of Ni_0.5Al_0.25Ti_0.25 was estimated from the enthalpy results to be 6.8 kJ/mol. The lattice parameters and melting temperatures of these compounds are also reported.     

Phase Equilibria of the Al-Mo-Dy Ternary System at 873 K

The phase relationship in the Al-Mo-Dy ternary system at 873 K has been investigated mainly by means of x-ray powder diffraction and scanning electron microscopy. The existences of ten binary compounds (i.e. AlMo₃, Al₈Mo₃, Al₄Mo, Al₅Mo, Al₁₂Mo, AlDy₂, Al₂Dy₃, AlDy, Al₂Dy and Al₃Dy) and one ternary compound (Al₄₃Mo₄Dy₆) have been confirmed. A new ternary compound Al₄Mo₂Dy (with a similar structure of the reported Al₄Mo₂Er) was found in the system. The 873 K phase diagram of this system consists of 15 single-phase regions, 29 two-phase regions and 15 three-phase regions. The maximum solid solubility of Al in AlMo₃ and Al₈Mo₃ is about 6 and 5 at.%, respectively.     

The Phase Relations Studies of Mg-Zn-RE at 553 K Coupling with Diffusion Triple Technique and Frist Principle Calculations

The isothermal sections of Mg-Zn-RE(Nd,Gd) ternary system at 553 K were measured with the help of diffusion triple technique. The results show that they were at metastable equilibrium instead of the final equilibrium state. Three ternary phases T1, T3 and T4 in Mg-Zn-Nd system have been detected. Specially, T3 was found out to be an independent ternary phase instead of a binary phase Mg₃Nd with very large solubility of Zn. Twelve tri-phases that reached local equilibriums have been identified in Mg-Zn-Nd system at 553 K. Two ternary compounds, W and I, have been found. The binary phases, Mg₅Gd and Mg₃Gd, have a solution of 3.0 at.% and 4.3 at.% Zn, respectively. The phase T-Mg₁₂RE type found in Mg-Zn-Nd agrees with the calculated result from First-principle.     

Experimental Phase Diagram of the Al-Er-Zr Ternary System

The phase diagram of the Al-Er-Zr ternary system at 773 K has been experimentally investigated by means of x-ray powder diffraction (XRD), differential thermal analysis (DTA) and scanning electron microscopy (SEM) with energy dispersive analysis (EDX). The existence of 13 binary compounds, i.e. Al₃Zr, Al₂Zr, Al₃Zr₂, AlZr, Al₃Zr₄, Al₂Zr₃, AlZr₂, AlZr₃, Al₃Er, Al₂Er, AlEr, Al₂Er₃ and AlEr₂ was confirmed. It is proved that the phases Al₃Zr₅ and Al₄Zr₅ do not exist at 773 K. The isothermal section consists of 16 single-phase regions, 29 binary-phase regions and 14 ternary-phase regions. The maximum solid solubility of Zr in Al₃Er, Al₂Er, AlEr, Al₂Er₃ and Er is about 9, 14, 4.5, 5.4, and 12 at.% Zr, respectively. No remarkable solid solubility could be found in the other compounds of this ternary system at 773 K. No ternary compound is found in the present work.     

450?°C Isothermal Section of the Al-V-Zn System

The 450?°C isothermal section of Al-V-Zn ternary system has been determined experimentally by means of optical microscopy, scanning electron microscopy coupled with energy-dispersive spectrometric, and x-ray diffraction. A new ternary compound named T, containing 8.2-9.9?at.% V, 12.1-27.4?at.% Zn, is positively identified for the first time in this study. The T phase only equilibrates with Al₃V, ??-Al, and L-Zn. Experimental results indicates that the maximal solubility of Al in VZn₃ is 25.2?at.%. The maximum solubility of Zn in ??-V is 5.7?at.%. The Zn solubility in Al-V compounds (Al₈V₅, Al₃V, Al₂₃V₄, Al₄₅V₇, and Al₂₁V₂) is 10.6, 9.2, 1.2, 0.6, and 0.4?at.%, respectively. The maximum solubility of Al in V is 41.0?at.%. Nine three-phase regions have been confirmed experimentally in this ternary system.     

Creep resistant Mg-Al-Ca alloys: Computational thermodynamics and experimental investigation

The thermodynamic properties of the ternary Mg-Al-Ca system are investigated in this article, based on the Al-Ca, Al-Mg, and Ca-Mg binary systems. The equilibrium phases in the Mg-Al-Ca alloys studied are the primary magnesium matrix and Cl5-Al ₂ Ca, as indicated by the calculated ternary phase diagrams. The experimental results are in good agreement with the thermodynamic calculations using Thermo-Calc software. For more information, contact A.A. Luo, General Motors Research and Development Center, Materials and Processes Lab, 30500 Mound Road, Warren, Michigan 48090-9055; (586) 986-8303; fax (586) 986-9204; e-mail alan.luo@gm.com     

Effect of heat treatment on the intermetallic layer of cold sprayed aluminum coatings on magnesium alloy

Dense and thick pure aluminum coatings were deposited on AZ91D-T4 magnesium substrates using the cold spray process. Heat treatments of the as-sprayed samples were carried out at 400 °C using different holding times. The feedstock powder, substrate and coating microstructures were examined using optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) as well as Vickers microhardness analysis. The results demonstrate that aluminum coatings having dense and uniform microstructure can be deposited successfully using a relatively large feedstock powder. It has been identified that the intermetallics Al₃Mg₂ (γ phase) and Mg₁₇Al₁₂ (β phase) were formed at the coating/substrate interface during heat treatment. The growth rate of these intermetallics follows the parabolic law and the γ phase has a higher growth rate than the β phase. The thickness of the Mg₁₇Al₁₂ and Al₃Mg₂ intermetallic layers has reached 83 μm and 149 μm, respectively. This result is almost 45% higher than what has been reported in the literature so far. This is attributed to the fact that T4 instead of as cast Mg alloy was used as substrate. In the T4 state, the Al concentration in the Mg matrix is higher, and thus intermetallic growth is faster as less enrichment is required to reach the critical level for intermetallic formation in the substrate. The AZ91D-T4 magnesium substrate contains single α phase with fine clusters/GP-zones which is considered beneficial for the intermetallic formation as well as the intimate contact between the coating/substrate interface and the deformed particles within the coating.     

Isothermal section of the Al-Dy-Ge ternary system at 673 K

The isothermal section of the phase diagram of the Al-Dy-Ge ternary system at 673 K has been investigated by X-ray powder diffraction and scanning electron microscope equipped with energy dispersive X-ray spectroscopy in backscattered electron imaging modes. The existence of thirteen binary compounds including Dy₃Ge₄ in the system Dy-Ge has been confirmed. Four ternary compounds, namely AlDyGe, Al₃Dy₂Ge₄, AlDy₂Ge₃, and AlDy₂Ge₂ were observed, and five new ternary compounds, i.e., Al_0.33DyGe₂, AlDy₂Ge₆, Al₂DyGe₂, AlDy₃Ge₃, and Al_3−xDy₁₁Ge_7+x (x ≤ 0.7), and one pseudo-binary compound Al_3−xDyGe_x were found in this system at 673 K. The maximum solid solubility of Ge in the pseudo-binary compounds Al_3−xDyGe_x is about 7.5 at.% with x = 0.3 at 673 K.     

The isothermal section of the phase diagram of Ce-Mg-Zn ternary system at 470 K

The isothermal section of the phase diagram of Ce-Mg-Zn ternary system at 470 K in a full concentration range was built, and a formation of seven ternary compounds was observed. For five ternary compounds: τ₁ - Ce₃(Zn_0.863Mg_0.137)₁₁ (Immm space group, La₃Al₁₁ structure type), τ₃ - CeMg_1+xZn_2−x (Fm-3m, MnCu₂Al), τ₄ - CeMg_2.5Zn_4.5 (P6/mmm, TbCu₇), τ₅ - Ce₃Mg₁₃Zn₃₀ (P6₃/mmc, Sm₃Mg₁₃Zn₃₀) and τ₇ - Ce₂₀Mg₁₉Zn₈₁ (F-43m, own structure type) the crystal structures were investigated. The crystal structures of CeMg_1−xZn_x continuous solid solution and of CeMg_12-xZn_x and CeMg_3-xZn_x limited solid solutions were studied more precisely by the X-ray single crystal and powder diffraction, and also using the WDS and EPMA techniques. The Ce-Mg-Zn ternary phases are structurally related to the binary phases of RE-Mg and RE-Zn (RE - rare-earth metals) systems.     

Phase Equilibria of the Al-Co-Zn System at 450 °C

The 450 °C isothermal section of the Al-Co-Zn ternary system was determined experimentally by means of scanning electronic microscopy coupled with wave dispersive x-ray spectroscopy, and x-ray powder diffraction. Nine three-phase regions have been confirmed experimentally. The liquid phase is in equilibrium with all Al-Co compounds except Al₃Co. The maximum solubility of Zn in AlCo, Al₅Co₂, Al₉Co₂ and Al₁₃Co₄ is 8.76, 18.14, 1.24, 8.97 at.%, respectively. The Al solubility in the Co-Zn compounds (γ₂, γ₁, γ, β₁) is very small, no more than 0.14, 0.28, 0.32, and 0.62 at.%, respectively. No true ternary compound was found in the present study.     

Thermodynamic Assessments of the Al2O3-Al4C3-AlN and Al4C3-AlN-SiC Systems

A thermodynamic dataset for the Al₂O₃-Al₄C₃-AlN system was reassessed and that of the Al₄C₃-AlN-SiC system was developed in present study for the first time based on available literature data using the CALPHAD approach. In the Al₂O₃-Al₄C₃-AlN system and its subsystems the liquid was described as single phase using the partially ionic liquid model $ ({\text{Al}}^{3 + } )_{P} ({\text{Va,AlC}}_{3/4} ,{\text{AlO}}_{3/2} , {\text{AlN}},{\text{O}}^{2 - } ,{\text{N,C}})_{Q} $ , which covers compositions from the metallic liquid to the oxide, carbide and nitride liquids. The compound energy formalism was used for modeling of the solid phases in both studied systems. Ternary phases ?? and ?? of the Al₄C₃-AlN-SiC system were treated as stoichiometric compounds. A four sublattice model was proposed in order to describe the ??-solid solution forming between the isostructural Al₅C₃N and Al₄SiC₄ binary phases. Using the derived datasets the isothermal sections at 1600, 2273 and 2373?K for the Al₂O₃-Al₄C₃-AlN system and at 2133?K for the Al₄C₃-AlN-SiC system were constructed. The calculated phase diagrams of both ternary systems were compared with the available experimental data.     

Crystal structure and magnetic properties of the new ternary actinide compounds AnPd5Al2 (An = U, Np)

We report the crystal structure and magnetic properties of new ternary actinide compounds UPd₅Al₂ and NpPd₅Al₂. Both compounds crystallize in the body-centered tetragonal ZrNi₂Al₅-type tetragonal structure (I 4/mmm). Although the magnetic susceptibility of both compounds follows the Curie–Weiss behavior at high temperature, no magnetic phase transition was observed. UPd₅Al₂ has a nonmagnetic ground state where the magnetic susceptibility saturates at low temperature, while NpPd₅Al₂ superconducts below 4.9 K as reported recently.