Ternary Intermetallic Phases Research Articles

Phase equilibria and thermodynamics of the Mg-Si-Li system and remodeling of the Mg-Si system

The ternary Li-Mg-Si phase relations were established using high-purity samples prepared by levitation melting. Analysis was done using x-ray powder diffraction (XRD), optical metallography, and differential thermal analysis (DTA) in customized sealed tantalum crucibles. Three ternary intermetallic phases were confirmed in this system: τ1 (Li8MgSi6), τ2 (Li12Mg3Si4), and τ3 (Li2MgSi). The LiMg2Si phase reported previously is not a separate phase but the interstitial solid solution of Li in the binary Mg2Si phase, LixMg2Si, at the maximum x ≈ 0.91 ± 0.05. Ternary liquidus data and phase transformations were also measured. A thermodynamic assessment of the ternary Li-Mg-Si system was worked out in parallel to the experimental study and used to select the relatively small number of our key experiments. The final consistent thermodynamic description is well supported by the present experimental data. It was found that the published thermodynamic parameter sets for the binary Mg-Si subsystem produce an artificial inverted liquid miscibility gap at higher temperatures. This system was remodeled to obtain data that could be reliably extrapolated to various temperatures and the ternary system. The experimentally supported calculated phase equilibria in the entire composition and temperature range of the Li-Mg-Si system are presented, including the liquidus surface and invariant reactions. Gradual changes in a monovariant eutectic/peritectic reaction type occur in this system. The intricacies involved due to solid solutions and the failure of the classic tangent criterion are discussed for some ternary alloys.

Dy—Sb—Si System at 1100 K and Ternary Intermetallic Phases in the Dy—Sb—Si and Gd—Sb—Si Systems.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Crystallisation of an amorphous Al 75Ni 21Y 4 alloy melt-spun ribbon

A new metastable ternary intermetallic phase having a hexagonal crystal structure, with a=0.858±0.017 nm and c=0.924±0.018 nm, has been identified in the Al–Ni–Y alloy system. This metastable phase was observed to form via a polymorphic crystallisation process from the amorphous phase in an Al 75Ni 21Y 4 alloy melt-spun ribbon, in competition with a fully coupled transformation product consisting of the equilibrium phases Al 3Ni and Al 16Ni 3Y.

Site preference in NiAl—determination by thermal conductivity measurement

A contour map of thermal conductivity in a ternary intermetallic phase characterizes the direction of the contour ridge, and the ridge direction has been demonstrated to be a reliable indication of site preference of ternary elements in an intermetallic compound. Site preferences of fifteen kinds of ternary elements in NiAl are determined from the ridge direction of thermal conductivity contours in ternary β phase. It is found that V, Nb, Ta, Mo, Fe, Ru, Co and Pt substitute preferentially for nickel, while Ti, Mn, Ga, Si and Ge for aluminum, and Cr and Cu occupy both nickel and aluminum sites.

Die soldering: Mechanism of the interface reaction between molten aluminum alloy and tool steel

Die soldering is the result when molten aluminum sticks to the surface of the die material and remains there after the ejection of the part; it results in considerable economic and production losses in the casting industry, and is a major quality detractor. In order to alleviate or mitigate die soldering, one must have a thorough understanding of the mechanism by which the aluminum sticks to the die material. A key question is whether the die soldering reaction is diffusion controlled or interface controlled. A set of diffusion couple experiments between molten aluminum alloy and the ferrous die was carried out. The results of the diffusion couple experiments showed that soldering is a diffusional process. When aluminum comes in contact with the ferrous die material, the iron and the aluminum atoms diffuse into each other resulting in the formation of a series of intermetallic phases over the die material. Initially iron and aluminum react with each other to form binary iron-aluminum intermetallic phases. Subsequently, these phases react with the molten aluminum to further form ternary iron-aluminum-silicon intermetallic phases. Iron and aluminum have a great affinity for each other and the root cause of die soldering is the high reaction kinetics, which exists between iron and aluminum. Once the initial binary and ternary intermetallic phase layers are formed over the die material, the aluminum sticks to the die due to the abnormally low thermal conductivity of the intermetallic phases, and due to favorable interface energies between the intermetallic layers and aluminum. The experimental details, the results of the interface reactions, and the analysis leading to the establishment of the mechanism giving rise to die soldering are reviewed discussed.

Creep and microstructure of magnesium-aluminum-calcium based alloys

This article describes the creep and microstructure of Mg-Al-Ca-based magnesium alloys (designated as ACX alloys, where A stands for aluminum; C for calcium; and X for strontium or silicon) developed for automotive powertrain applications. Important creep parameters, i.e., secondary creep rate and creep strength, for the new alloys are reported. Creep properties of the new alloys are significantly better than those of the AE42 (Mg-4 pct* Al-2 pct RE**) alloy, which is the benchmark creep-resistant magnesium die-casting alloy. Creep mechanisms for different temperature/stress regimes are proposed. A ternary intermetallic phase, (Mg,Al)2Ca, was identified in the microstructure of the ACX alloys and is proposed to be responsible for the improved creep resistance of the alloys.

Thermodynamics of B2 intermetallic compounds with triple defects: a Bragg-Williams model for (Ni,Co)Al

Applying the Bragg-Williams approximation, a pair interaction model has been developed for describing the composition and temperature dependence of thermodynamic properties of ternary intermetallic B2 phases. Taking the activities and the integral enthalpies of formation as input data, values for the enthalpy and the entropy of bonds between atoms have been obtained. An analytical expression has been derived for the dependence of the concentration of point defects (vacancies and antistructure atoms) on composition and temperature. The model has been applied successfully to the available experimental data for the Ni-Al, Co-Al, and Ni-Co-Al systems. It has been shown that the values calculated accordingly for the effective enthalpy (and entropy) of formation of vacancies agree well with those from experimental observations and theoretical ab initio calculations.

Effects of Cu and Ni additions to eutectic Pb–Sn solders on Au embrittlement of solder interconnections

Effects Cu and Ni additions on Au embrittlement of eutectic Sn–Pb solder interconnections during a solid-state aging treatment were evaluated using a ball shear testing method. The addition resulted in a formation of Au-containing ternary intermetallic compounds, either Au–Sn–Cu or Au–Sn–Ni phase, inside the solder matrix during aging treatment. The fracture energy of the solder interconnection containing 2.9 wt% Cu remained almost the same up to 200 h of aging treatment at 150 °C, demonstrating the possibility of suppressing the Au embrittlement by forming ternary intermetallic phases inside the solder matrix.

Ferrimagnetism in Tb 3Co 8Sn 4 intermetallic compound

AC and DC magnetic measurements were performed on the ternary intermetallic phase Tb 3Co 8Sn 4. The compound shows a ferrimagnetic transition at T C=91 K. From the imaginary part of the AC susceptibility a second broad peak was detected at T g=28 K and ascribed to a transition to a spin glass state. Zero field cooled (ZFC) and field cooled (FC) magnetization measurements at μ 0 H=0.05 Tesla (T) confirmed the reentrant spin glass state below 30 K. The hysteresis cycle, obtained from magnetization measurements at 5 K, allows to obtain the remanence ( B r=0.43 T) and the coercive field ( H C=159.2 kA/m). The experimental data were analysed in the framework of the Molecular Field Theory.

Phase equilibria and intermetallic phases in the Ni-Si-Mg ternary system

The Ni-Si-Mg ternary phase diagram has been established after homogenization and slow cooling to room temperature. The chemical compositions of the alloys and their phases were obtained using fully quantitative energy dispersive X-ray spectroscopy (EDS) with standard spectrum files created from intermetallic compounds Mg2Ni and Ni2Si. The following intermetallic phases have been observed: (a) four new ternary intermetallic phases, designated as ν, ω, μ, and τ, (b) a ternary intermediate phase Mg(Ni,Si)2 based on the binary MgNi2 phase containing Si; (c) three ternary intermetallic phases, η, κ, and ζ, previously reported by the present authors;[10] and (d) Mg2SiNi3 (Fe2Tb type),[9] previously reported by Noreus et al.[8] The MgNi6Si6 phase, which was also previously reported,[7] was not observed at the corresponding composition in the present work. However, the MgNi6Si6 phase reported as being of hexagonal symmetry (Cu7Tb type),[9] with the lattice parameters a=0.4948 nm and c=0.3738 nm, possibly corresponds to the μ phase (Mg(Si0.48Ni0.52)7) discovered in the present work. The lattice structure of the newly discovered ω phase was determined with the help of the X-ray indexing program TREOR (developed by Werner et al.[13]) to be a hexagonal structure of the Ag7Te4 type ((Mg0.52Ni0.48)7Si4) with the lattice parameters a=1.3511 nm and c=0.8267 nm.

Thermodynamic assessment of the Al-Fe-Si system

The phase equilibria and thermodynamic properties of the ternary Al-Fe-Si system were analyzed and a complete thermodynamic description of the ternary system was obtained. The thermodynamic descriptions of the three binary systems were taken from the literature. Most of the binary intermetallic phases, except Al13Fe4(ϑ), FeSi2-L, and FeSi2-H, were assumed to have no ternary solubility. Based on the experimental data, seven stable ternary intermetallic phases were considered in the system. Two of them were treated as semistoichiometric compounds with homogeneity ranges for Al and Si, and the others were treated as stoichiometric compounds. Reasonable agreement was obtained between calculation results and experimental information in the ternary system.

Metallograpiuc Study of Gasar Porous Magnesium

ABSTRACTOne of the promising techniques for making porous metals is the so-called GASAR process. In principle, the process affords considerable control over pore size, shape, and distribution. However, in practice, the pore microstructure is difficult to control, and a clearer understanding of microstructural evolution would be helpful. In this study, we undertake a detailed microstructural study of a porous Mg and AZ31 Mg alloy synthesized by the GASAR process. Microscopic studies demonstrated the presence of different pore size ranges. The pore distribution depended on the distance from the chill end of ingots. TEM observations revealed apparent crack lines (gas tracks) near the pores and ternary intermetallic phases in the alloy.

Indentation microcracking and toughness of newly discovered ternary intermetallic phases in the NiSiMg system

Indentation microcracking pattern and fracture toughness of the newly discovered cubic η and hexagonal κ intermetallic phases in the Ni-Si-Mg system, were studied. It is shown that the determination of the crack system as being either Palmqvist or halfpenny by simple polishing away of the indented surface is unreliable due to the existence of the core zone with compressive stresses. In the complex cubic η phase a serial sectioning method revealed so-called pseudo half-penny crack system, in the entire 200 to 2000 g range of indentation loads. On the contrary, at 200 and 500 g loads, the hexagonal κ phase develops the ‘kidney-shaped’ crack system which resembles the Palmqvist crack system but this phase develops the pseudo halfpenny crack system at 2000 g load. All the pseudo half-penny cracks, regardless of the applied load, at which they were formed, contain a compressive stresses core zone up to 40–50 μm deep. This is the first experimental evidence of such a zone being formed during microhardness indentation of intermetallics. In general, the existence of the indentation core zone in the pseudo halfpenny cracks does not seem to change the crack length-load characteristic of the halfpenny cracks allowing the use of existing equations for the penny-shaped crack system to calculate fracture toughness. However, equally reasonable indentation fracture toughness values are also obtained by using the Shetty et al. (Journal of Material Science , 1985, 20 , 1873) model, based on the Palmqvist crack system, which is modified in the present work. Our modification takes into account the indentation size effect (ISE) and yields results of K IC independent of indentation loads. Indentation fracture toughness calculated for the η and κ phases from the selected equations found in the literature for ceramics gives quite diverse results. The most reasonable values of indentation fracture toughness are obtained from the Palmqvist-type cracking using modified Shetty et al. model and from the half-penny-type cracking using Evans and Charles ( Journal of the American Ceramic Society , 1976, 59 (7/8), 371) and Lawn and Evans ( Journal of Material Science , 1977, 12 , 2195) models. The indentation fracture toughness values (customarily designated K IC ) calculated from the above models are on the order of 1.4−1.8 MPa m 1 2 for the η and 1.8−2.5 MPa m 1 2 for the κ phases.

Ln3Au2Al9 (Ln  Dy, Tb): Heteronuclear versus Homonuclear Bonding in Intermetallic Phases

A variant of the BaAl4 structure, the α-La3Al11 structural type is observed upon crystallization of the new ternary intermetallic phase Ln3Au2Al9 (Ln = Dy and Tb). Calculations of the electronic structure were used to investigate the characteristics of Au and Al atoms within the framework. The gray atoms in the picture of the structure prefer heteronuclear AuAl contacts over homonuclear AlAl and AuAu contacts.

Fatigue properties of high strength steels containing retained austenite : Yokoi, T., Kawasaki, K., Takahashi, M., Koyama, K. and Mizui, M. JSAE Review (1996) 17 (2), 210–212

The formation enthalpy of binary AlNi and AlNi3 and ternary Al2NiTi, AlNiTi and AlNi2Ti intermetallic phases was determined by the solution calorimetric method. The phases were prepared by the levitation technique and by melting metals in a glove-box operating with high purity argon. After the preparation, all phases were identified by X-ray diffraction (XRD) and the quantitative analysis was performed by means of a scanning electron microscope (SEM EDS). The formation enthalpies measured at room temperature for the binary and ternary phases are as follows: −66.3 ± 1.7 kJ/mole of atoms for AlNi, −40.5 ± 1.6 kJ/mole of atoms for AlNi3, −40.7 ± 1.8 kJ/mole of atoms for Al2NiTi, −56.9 ± 1.1 kJ/mol of atoms for AlNiTi and −72.1 ± 1.2 kJ/mole of atoms for AlNi2Ti.Additionally, for the AlNiTi phase, the measurements were conducted at the temperature of 1133 K and the determined formation enthalpy was found to equal −56.5 ± 2 kJ/mol of atoms. The very near values obtained at room and elevated temperature point to the fact that it is independent of temperature.

A study of micropyretic reactions in the Mo–Si–Al ternary system

Micropyretic synthesis technique employs self-sustaining exothermic (combustion) reactions for the preparation of various ceramic, intermetallic, and composite materials. In the present work, the combustion reactions of Mo and Si with Al additions have been systematically studied. The atomic mixtures of the reactant powders are chosen to be Mo + (2 − x)Si + xAl with x = 0−0.4. In comparison with the Mo + 2Si reaction which leads to the formation of MoSi2, the substitution of Al for Si decreases the sample ignition temperature, but increases the intensity of the combustion reactions. In addition, the substitution of Al for Si results in the formation of a ternary intermetallic phase, called molybdenum alumino-silicide Mo(Si, Al)2, in the synthesized product. When the content of Al in the reactant mixtures reaches 0.4, nearly single phase Mo(Si, Al)2 is obtained and no MoSi2 is detected in the reaction product. These influences are analyzed by using x-ray diffraction (XRD), scanning electron microscopy (SEM), and differential thermal analysis (DTA). The effect of Al additions on the reaction mechanism is also discussed.

The Al–Cr–Fe system–Phases and phase equilibria in the Al-rich corner

An isothermal section for the Al–Cr–Fe system at 1000 °C has been experimentally determined. From metallography, electron microprobe analyses and X-ray investigations on quenched samples the phase equilibria in the Al-rich corner of this system were established. No ternary intermetallic phases were found. But the binary compounds—and here especially those intermetallic phases originating in the Al–Cr subsystem—have large solid solubility ranges for the third element. This has a marked influence on the lattice constants, which were determined for all phases. In addition two X-ray spectra are presented. One for Al 8Cr 5, where three quarters of Cr can be substituted by Fe and for Al 4Cr, which was found to have a different crystallographic structure than described elsewhere.

A thermodynamic description for the ternary Al-Mg-Cu system

A thermodynamic description for the ternary Al-Mg-Cu system was obtained based on the descriptions of its three constituent binaries and ternary phase equilibrium and thermodynamic data available in the literature. All binary intermetallic phases are assumed to have negligible ternary solubility. There are five ternary intermetallic phases; three of them are taken to be line compounds and two are assumed to be semistoichiometric phases. In view of the extensive experimental data available in the Al-rich corner, particularly for the Al-rich ternary eutectic, the objective of this study was to develop a thermodynamic description that allows us to quantitatively calculate the phase equilibria in the Al-rich corner. The calculated phase equilibria in the Mg-rich corner may not be as good as those in the Al-rich corner, and those in the Cu-rich corner should be topologically correct and serve as a guide for materials researchers to carry out key experiments in the future to establish the phase equilibria in that portion of the system. Nevertheless, in the absence of additional data, the calculated phase equilibria in the Cu-rich corner can be used with caution.

Formation of Ternary Intermetallic Phase by Mechanical Allloying of Al-Fe-Ge

Formation of Ternary Intermetallic Phase by Mechanical Allloying of Al-Fe-Ge

Phase Equilibria in the Ni-Al-Ta System

Phase equilibria in the Ni-Al-Ta system were determined at 1000 and 1250°C. From metallography, X-ray diffraction and electron probe microanalysis (EPMA), two isothermal sections for Ta contents < 50 at. % were set up. The stability ranges of the Laves phase NiAlTa and the Heusler phase Ni 2 AlTa were fixed and that of Ni 6 AlTa is confirmed. Several other ternary intermetallic phases, which had been reported in the literature, are not confirmed. Lattice constants are given for all phases studied. For those phases with a large solid solubility range, i.e. NiTa and NiAlTa, they are given as a function of composition.