Ternary Intermetallic Phases Research Articles

Phase equilibria in the Fe–Al–Nb system: Solidification behaviour, liquidus surface and isothermal sections

The Fe–Al–Nb phase diagram including isothermal sections at 1000, 1150, and 1300 °C as well as the liquidus surface and corresponding reaction scheme was studied experimentally by a combination of scanning electron microscopy (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), and differential thermal analysis (DTA). No genuinely ternary intermetallic phase exists in the system, but the two Fe–Nb phases NbFe2 (C14-type Laves phase) and Fe7Nb6 (μ phase) have extended homogeneity ranges in the ternary system, where large amounts of Fe can be substituted by Al in both cases. The solubility of the third element was studied for all binary phases and the effect on the lattice parameters is discussed. From analysis of the as-cast microstructures and DTA experiments, the liquidus surface including all invariant reactions as well as the occurring solid state reactions were established. Three ternary eutectics, one eutectoid, and two peritectic reactions were found, and the list of invariant points is completed by seven U-type reactions.

Effect of the composition of Al-Li alloys on the quantitative relation between the δ′(Al3Li), S1(Al2MgLi), and T1(Al2CuLi) phases

Al-Li alloys are considered. A quantitative approach to the determination of the ratio of the fractions of the binary and ternary intermetallic phases in Al-Mg(Cu)-Li alloys is developed on the basis of chemical and phase composition balance equations and the experimentally measured lattice parameter of the α solid solution. The ratio of the fractions of the δ′(Al3Li) and S1(T1) phases in Al-Mg(Cu)-Li alloys is shown to be determined by the ratio of the mole fractions of Li and Mg(Cu). Equations are proposed for calculating the weight fractions of the S1(Al2MgLi), T1(Al2CuLi) and δ′(Al3Li) phases in domestic and foreign Al-Mg-Li alloys 1420, 1424, 5090 and Al-Cu-Li alloys 1440, 1460, 1461, 1441, 1469, 2090, 2095, 8090, and Weldalite 049.

Formation of nanometer scale intermetallic phase at interface of aluminum-to-steel spot joint by welding–brazing process

Interfacial microstructure, joint strength and crack propagation passage of fusion weld–brazed IF steel/Al 5754 joints were investigated. Nanometer scale intermetallic τ5 compound layer and needle-like τ6 ternary phase were observed at the interface with a heat input below 0.27kJ/cm. Joint shear strength of 150–200MPa was obtained, which resulted from the formation of an ultra-thin ternary intermetallic phase and the lack of the more brittle binary intermetallic phase at the steel/solidified filler alloy interface.

Microstructural Evolution and Mechanical Behaviour of Metastable Cu–Zr–Co Alloys

Three different Cu–Zr–Co alloys, namely Cu 40 Zr 37.5 Co 22.5 , Cu 42.5 Zr 45 Co 12.5 and Cu 49 Zr 49 Co 2 , were obtained by rapid cooling. The microstructure and phase formation of as-cast rods with diameters of 2 mm are compared with those of the respective ingots. An increasing Co content stabilises the B2 CuZr phase and leads to the precipitation of a ternary Cu–Zr–Co phase. The variation of the cooling rate affects the size of the B2 dendrites as well as the volume fraction and the morphology of the interdendritic phases. The mechanical properties were determined in compression and all alloys show a certain plastic deformability despite the presence of several binary and ternary intermetallic phases. The deformation mechanisms are discussed on the basis of the microstructures and the constituent phases.

Microstructural Investigation and Phase Relationships of Fe-Al-Hf Alloys

The effect of Hf addition on microstructures, phase relationships, microhardness, and magnetic properties of Fe50Al50−nHfn alloys for n = 1, 3, 5, 7, and 9 at. pct has been investigated. At all investigated compositions, the ternary intermetallic HfFe6Al6τ1 phase forms due to the limited solid solubility of Hf in FeAl phase and tends to develop a eutectic phase mixture with the Fe-Al-based phase. The Hf concentration of the eutectic composition is found to be 7 at. pct from the microstructural examinations and the eutectic phase transition temperature is determined as 1521 K (1248 °C) independent of Hf amount by differential scanning calorimetry measurements. Furthermore, the enthalpies and activation energies (based on Kissinger and Ozawa methods) of eutectic phase transitions are reported. The minimum activation energy is calculated for the fully eutectic composition. Moreover, variation of the microhardness of Fe-Al-based alloys as a function of the Hf content is investigated, and its dependence on the thermal history of the alloys is explained.

On the 500°C isothermal section of the ternary Eu–Ag–Ga system up to 33.3 at.% Eu

• Isothermal section of the Eu–Ag–Ga (0–33.3 at.% Eu) system at 500 °C. • Identification six new ternary intermetallic phases. • Crystal structure determination of the Eu 2 Ag 13.6–13 Ga 3.3–4 . The isothermal section of the ternary Eu–Ag–Ga system has been studied at 500 °C for the 0–33.3 at.% Eu concentration region. X-ray diffraction techniques, optical microscopy and scanning electron microscopy, complemented with energy dispersive X-ray spectroscopy, were used to identify the phases and characterize their crystal structures and compositions. The crystal structure of selected phases has been refined using powder X-ray diffraction data. This study indicates the formation of six new intermetallic phases in the explored region: EuAg 0.14 Ga 2.86 (own type, related to CeNiSi 2 type), EuAg 2.8 Ga 1.8 (YbAg 2.5 Ga 2.1 type), Eu 4 Ag 14.7 Ga 7.6 (Sc 4 Cu 14.76 Ga 7.51 type), Eu 4 Ag 11.3 Ga 5.7 (own type), Eu 2 Ag 13.6–13 Ga 3.3–4 (Th 2 Zn 17 type) and EuAg 3.2 Ga 0.8 (unknown type).

Contribution to the investigation of the ternary Eu–Ag–Al system

The interaction of the components from the Eu–Ag–Al system at 500 °C, in the concentration region of 0–33.3 at.% Eu, was investigated by X-ray diffraction, metallographic and microprobe analysis. Besides the known ternary intermetallic phases (EuAg3+xAl8−x and EuAg4+xAl7−x), six new ones (EuAg6+xAl7−x, Eu2Ag15−xAl2+x, Eu3Ag13−xAl8+x, EuAg1−xAl2+x, EuAg1+xAl2−x and EuAg1−xAl1+x) were revealed to be stable at the temperature investigated. Furthermore, extended solid solutions based on the binary EuAl4, EuAl2, EuAg5 and EuAg2 compounds were also found. The crystal structures of selected phases were studied by means of powder X-ray diffraction techniques and are briefly discussed.

Enthalpy of formation of intermetallic phases from Al–Ni and Al–Ni–Ti systems

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.

Study of ternary complex Al—Mg—Ag intermetallides using Precession Electron Diffraction

Three ternary intermetallic phases were revealed in Mg-20 at%Al—20 at%Ag alloy: Mg59Al34Ag7 (body-centered cubic, a = 10.2 Å, probably isotypical to Mg17Al12 phase); Mg62Al11Ag27 (body centered cubic, a = 14.5 Å) and new Mg19Al13Ag6 compound. The geometry and the symmetry of the unit cell of these phases were investigated by electron diffraction methods. It was found that the structure of the new Mg19Al13Ag6 phase belongs to the orthorhombic crystal system with lattice parameters of a = 8.87, b = 16.48 and c = 19.48 Å. The space group was evaluated by Precession Electron Diffraction technique in “descan-off” mode as Pbcm (No. 57).

Synthesizing Nanostructured Ni75Mg16.66Y8.34 (at%) Powder by Solid State Reaction and Mechanical Milling

In this study, nanostructured Ni75Mg16.66Y8.34 (at%) catalyst powder was prepared using two methods. In method one, the pure elemental powders were subjected to high energy ball milling for 5 to 25 h with a ball to powder weight ratio of 20. In method two, the pure elemental powders were pressed, heat treated at 800°C for 8 h (solid state reaction); then, they were ball milled for 2, 7.5 and 10 h, similarly to the first method. Finally, morphology, phases, particle size, crystallite size, and lattice strain values of the prepared powder alloys were determined by X-ray diffraction (XRD) and scanning electron microscope (SEM) methods. The XRD patterns showed that the Mg2Ni9Y ternary intermetallic phase was not formed in the sample prepared by method one; however, that was formed in the samples prepared by the second method. The required milling time for preparing the samples with the same powder specifications by method two was about 50% less than the time required by method one. It was found that the Ni75Mg16.66Y8.34 (at%) powder with smaller particle size, smaller crystallite size, and higher lattice strain values could be prepared by combining solid state reaction and mechanical milling processes.

Thermodynamic Database for Mg Alloys—Progress in Multicomponent Modeling

Progress in systematic development of a thermodynamic database for Mg alloys with 21 components is reported. Models for multicomponent alloys are built in a methodical approach from quantitative descriptions of unary, binary and ternary subsystems. For a large number of ternary—and some higher—alloy systems, an evaluation of the modeling depth is made with concise reference to experimental work validating these thermodynamic descriptions. A special focus is on ternary intermetallic phase compositions. These comprise solutions of the third component in a binary compound as well as truly ternary solid solution phases, in addition to the simple ternary stoichiometric phases. Concise information on the stability ranges is given. That evaluation is extended to selected quaternary and even higher alloy systems. Thermodynamic descriptions of intermetallic solution phases guided by their crystal structure are also elaborated and the diversity of such unified phases is emphasized.

Soluble Zintl Phases A14ZnGe16 (A = K, Rb) Featuring [(η3-Ge4)Zn(η2-Ge4)]6– and [Ge4]4– Clusters and the Isolation of [(MesCu)2(η3,η3-Ge4)]4–: The Missing Link in the Solution Chemistry of Tetrahedral Group 14 Element Zintl Clusters

The number of Zintl phases containing polyhedral clusters of tetrel elements that are accessible for chemical reactions of the main-group element clusters is rather limited. The synthesis and structural characterization of two novel ternary intermetallic phases A(14)ZnGe(16) (A = K, Rb) are presented, and their chemical reactivity is investigated. The compounds can be rationalized as Zintl phases with 14 alkali metal cations A(+) (A = K, Rb), two tetrahedral [Ge(4)](4-) Zintl anions, and one anionic heterometallic [(Ge(4))Zn(Ge(4))](6-) cluster per formula unit. The Zn-Ge cluster comprises two (Ge(4)) tetrahedra which are linked by a Zn atom, with one (Ge(4)) tetrahedron coordinating with a triangular face (η(3)) and the other one with an edge (η(2)). [(η(3)-Ge(4))Zn(η(2)-Ge(4))](6-) is a new isomer of the [(Ge(4))Zn(Ge(4))](6-) anion in Cs(6)ZnGe(8). The phases dissolve in liquid ammonia and thus represent rare examples of soluble Zintl compounds with deltahedral units of group 14 element atoms. Compounds with tetrahedral [E(4)](4-) species have previously been isolated from solution for E = Si, Sn, and Pb, and the current investigation provides the "missing link" for E = Ge. Reaction of an ammonia solution of K(14)ZnGe(16) with MesCu (Mes = 2,4,6-(CH(3))(3)C(6)H(2)) in the presence of [18]-crown-6 (1,4,7,10,13,16-hexaoxacyclooctadecane) yielded crystals of the salt [K([18]-crown-6)](2)K(2)[(MesCu)(2)Ge(4)](NH(3))(7.5) with the polyanion [(MesCu)(2)Ge(4)](4-). This MesCu-stabilized tetrahedral [Ge(4)](4-) cluster also completes the series of [(MesCu)(2)Si(4-x)Ge(x)](4-) clusters, which have previously been isolated from solution for x = 0 and 0.7, as the end member with x = 4. The electronic structures of [(Ge(4))Zn(Ge(4))](6-) and [(MesCu)(2)Ge(4)](4-) were investigated in terms of a molecular orbital description and analyses of the electron localization functions. The results are compared with band structure calculations for the A(14)ZnGe(16) phases (A = K, Rb).

Analysis of dynamic segregation and crystallisation in Mg65Cu25Y10 bulk metallic glass using atom probe tomography

In order to develop an in-depth understanding of the flow behaviour and dynamic devitrification processes of metallic glasses in the supercooled liquid region, tensile testing of amorphous Mg65Cu25Y10 samples was carried out at temperatures from 150 to 170°C and at strain rates from 1×10−3s-1 to 1×10−2s−1. Tensile data showed a consistent and reproducible inflexion in flow stress at a particular strain that was largely independent of strain rate. This was followed by a dramatic increase in flow stress occuring prior to the determined onset times of static crystallisation. Samples were analysed using atom probe tomography and the results indicate that tensile straining of the initially homogeneous amorphous alloy results in segregation into two distinct glassy phases via a shear-related process, coincident with the maximum shear plane angle, followed by the evolution of regions corresponding to the composition of a number of equilibrium binary and ternary intermetallic phases.

Thermodynamic description of the Al–Cu–Y ternary system

Phase equilibria in the ternary Al–Cu–Y system have been analyzed by coupling the CALPHAD method and first-principles calculations, and a complete thermodynamic description was obtained. The thermodynamic descriptions of its three constituent binary systems were taken from the literature. Most of the binary intermetallic phases, except Al3Y, Al2Y, and Cu2Y, were treated to have zero solubility in the ternary system. Based on experimental data, eight stable ternary intermetallic phases were taken into consideration in the present work. Among them, three phases were treated as line compounds with large homogeneity ranges for Al and Cu. The others were treated as stoichiometric compounds. The calculated phase equilibria were in agreement with available experimental data.

Structural variations in the ternary system HfAl2−xCux (x = 0.2–1.0)

Synthesized ternary intermetallic phases HfAl2−xCux in a series with (x = 0.49, 0.88, 1.04) are characterized as Laves phase structures. X-ray diffraction revealed homogeneity within ranges 0.2 ≤ x ≤ 0.5 and 0.7 ≤ x ≤ 0.9 for structure types MgCu2 and MgNi2, respectively. When Cu atoms gradually replaced the Al atoms, the structure type altered in the sequence MgCu2 → MgNi2 → MgZn2, and the Kagomé nets were distorted with varied bond lengths. Measurements of physical properties revealed these phases to be metallic, with resistances 4.35 (x = 0.5), 5.85 (x = 0.7), and 6.50 (x = 0.9) mΩ cm, respectively, at temperature 300 K. The coloring schemes reveal that, upon increasing the proportion of Cu atoms, the stability of these phases correlated with the arrangements of the Al and Cu atoms. Calculated electronic structures indicate that the bonding character is consistent with the experimentally observed phase width.

Liquid Phase Bonding of 316L Stainless Steel to AZ31 Magnesium Alloy

The excellent corrosion resistance, formability and strength make stainless steels versatile for diverse applications. However, its high specific strength and good crashworthiness make it suitable for transportation and aerospace industry. On the other hand, the need to reduce the weight of vehicle and aerospace components has created renewed interest in the use of magnesium alloys. Due to their differences in physical and metallurgical properties, bonding of the 316L steel and AZ31 magnesium alloy using conventional fusion welding methods encountered many limitations. Therefore, the use of liquid phase forming interlayers is required to overcome the differences in their properties, eliminates the need for a high bonding pressure to achieve intimate contact between the bonded surfaces. Both Cu and Ni interlayers successively formed a eutectic phase with magnesium. The formation of intermetallics and Mg diffusion caused the eutectic phase to isothermally solidify with increasing bonding time. The formation of ternary intermetallic phases (γ1 and B2) impaired the bond shear strength particularly at the end of the isothermal solidification stage where no eutectic phase was observed. However, the joints showed a higher shear strength value of 57 MPa when bonding with Cu interlayer at 530°C for 30 min compared to 32 MPa when Ni interlayer was used at 510°C for 20 min.

Specific Heat Capacities of Some Ternary Aluminides

Two different methods were employed to prepare samples of the ternary intermetallic phase: AlNi2Ti, and of Al0.4Fe0.5Ni0.1, Al0.4Fe0.3Ni0.3, Al0.4Fe0.1Ni0.5 solid solutions, respectively. Alloys were then subjected to heat treatment for homogenization. Phase identification was made by XRD phase analysis and by the SEM BSE technique, and chemical composition was determined using the EDS method. Heat capacity measurements were made within a temperature range from 100 to 600 K using the DSC technique. Results were listed in tables and then fitted to a Kelley equation; an example of C p vs. T curve is given.

Eutectic bonding of austenitic stainless steel 316L to magnesium alloy AZ31 using copper interlayer

The eutectic bonding of magnesium alloy (AZ31) to austenitic stainless steel alloy (316L) was performed using pure Cu interlayers. The effect of hold time on the microstructural developments across the joint region and the related effect on bond shear strength were studied at a bonding temperature of 530°C. The bonding process took place through a sequential occurrence of solid-state diffusion of Cu into the magnesium alloy, eutectic phase formation, interlayer dissolution, and isothermal solidification. A (Mg–Cu–Al) ternary intermetallic phase formed within the joint and concentrated into the center of the bond during the solidification stage increasing the hardness value to a maximum average of VHN313 while the maximum recorded bond shear strength was 57 MPa achieving 69% of the AZ31 shear strength and about three to four times of the adhesive joints.

Experimental investigation of the Nd–Al–Si system

Abstract The isothermal section of the Nd–Al–Si ternary system at 500 °C has been investigated using differential thermal analysis, X-ray diffraction analysis, scanning electron microscopy and electron micro-probe analysis. Four ternary intermetallic compounds were confirmed: NdAl2Si2 (τ1), hP5-CaLa2O2 structure type, Nd2Al3Si (τ2), hP3-AlB2 structure type, NdAl1−xSi1+x, 0.25 ≤ x ≤ 0.3 (τ3), tI12-αThSi2 structure type and Nd2Al1−xSi1+x, 0 ≤ x ≤ 0.2, (τ5), oS8-CrB structure type. A new ternary intermetallic phase (τ4) was found: Nd4Al3Si3, orthorhombic oS20, isotypic with Pr4Al3Ge3.

Producing ternary intermetallic compounds powders by solid–liquid reaction ball milling

A novel mechanochemistry approach, defined as solid–liquid reaction ball milling, was applied to obtain single-phase Al–Cu–X (X = Fe, Co, and Ni) ternary intermetallic compound powders by reactions between milling medium (ball and cylinder) and liquid-state metals in certain temperature range, where the milling mediums made of metals with high-melting point and took part in the reaction as the solid-state reactants. Compared with the conventional mechanical milling technique, nanometer-sized intermetallic compound powders and some single-phase ternary intermetallic phases could be obtained at lower temperatures by the solid-state reaction ball milling. Furthermore, the reaction mechanisms of this mechanochemical approach have been discussed in details.