Formation of ordered nano-wire microstructures in thermoelectric Pb-Ag-Sb-Te

Regular arrays of nano-wire microstructures containing Ag₂Te rods with diameter <400 nm and inter-rod distance <1 μm are formed in a matrix of AgSbTe₂ + δ-Sb₂Te, which makes an ordered nano-wire composite thermoelectric material. This microstructure is formed during eutectic solidification processing. To understand and guide production of uniform bulk samples of this composite, the liquidus projection of quaternary Pb-Ag-Sb-Te system at 36.0 at.% Te isoplethal section is constructed experimentally, using quenched samples. A three-phase univariant reaction of the quaternary Pb-Ag-Sb-Te system, L → AgSbTe₂ + Ag₂Te + δ-Sb₂Te, is investigated, between a ternary-eutectic melt (Ag-40.0 at.% Sb-36.0 at.% Te) and a quaternary melt (Pb-22.0 at.% Ag-40.0 at.% Sb-36.0 at.% Te), at 496.1 °C and 503.9 °C, respectively. High-resolution transmission electron microscopy confirms that these three phases are simultaneously present at the nanometer scale. Furthermore, unidirectional solidification experiments of the ternary eutectic alloy using the Bridgman method are carried out to examine the alloy’s solidification behavior.     

Glass forming ability and crystallization of Zr-Cu-Ag-Al-Be bulk metallic glasses

The glass forming ability of Zr₄₆Cu_37.64−xAg_8.36Al₈Be_x (x = 0, 6 and 10 at.%) bulk metallic glasses (BMGs) were significantly improved by Be addition. The critical size of amorphous rods can be over 35 mm diameter. The high GFA achieved is mainly due to the decrease of melting point and liquidus temperature, and suppression of the formation of crystalline phases during solidification from liquid state. The high stabilization with supercooled liquid regime of 115 K was found for the BMG with x = 10 at.%. Two independent exothermic events happen in x = 0 and 6 at.% BMGs, corresponding to the formation of primary crystalline phases Cu₁₀Zr₇ and AgZr, then transforming to final stable crystalline phases Zr₂Cu and AlCu₂Zr. However, in the x = 10 at.% BMG, the precipitation of primary phases and transformation to final stable phases are within the first exothermic event and the AlCu₂Zr phase is totally suppressed.     

Liquidus projection for the Mo-rich portion of the Mo–Si–B ternary system

The solidification behavior in the Mo-rich portion of the Mo–Si–B ternary system has been examined based on the microstructures of arc-cast alloys. Several solidification characteristics in the Mo-rich portion of the system have been identified using XRD, SEM and TEM. The liquidus projection in the Mo-rich portion includes six primary solidification reactions; five reactions originating from the Mo–Si and Mo–B binary sections (Mo, Mo₂B, βMoB, Mo₃Si and Mo₅Si₃) and one from the ternary-based (Mo₅SiB₂) T₂ phase. The liquidus surface in general descends from the high melting temperature Mo–B binary side to the lower melting temperature Mo–Si binary side. The solidification path of alloys with compositions in the T₂ phase region is always preceded by the peritectic reaction of βMoB+L⇒T₂. In addition, four Class II reactions (four-phase reactions) and one Class I reaction (invariant ternary eutectic reaction) have been identified. The extent of solidification segregation in alloys with compositions in the Mo(ss)+T₂ two-phase field is discussed as it pertains to materials processing.     

Thermodynamic modeling of Al–Ce–Mg phase equilibria coupled with key experiments

The ternary Al–Ce–Mg phase diagram was calculated using the Calphad method and investigated with selected key experiments. Arc melted alloys were annealed at 400 °C for 500 h and the phases were analyzed using quantitative X-ray powder diffraction (XRD). Differential thermal analysis (DTA) was also performed on an alloy with a composition near the ternary phase Al₁₃CeMg₆ (τ). Temperatures above 1000 °C could be attained due to a special sealing of the sample under argon by welding in a tantalum crucible to avoid evaporation and oxidation. Only with this procedure could reproducible and reliable DTA signals be obtained. The present experimental investigation and the consistent thermodynamic calculation show that the “ternary phase” Ce(Mg,Al)₂, seemingly isolated in the ternary at 400 °C, can be rationalized as a single solid solution phase between the binary end members if a larger temperature range and a solid state miscibility gap is considered. It is demonstrated that previously reported low values of ternary liquidus temperatures must be related to other phase equilibria. The actually found ternary liquidus temperatures are much higher and widely governed by the high melting compound Ce(Al,Mg)₂ and also by Al₁₁Ce₃ with primary solidification fields stretching far into the ternary system.     

Supplementary measurements of the primary crystalline phases of the Co-Ni-Sb and the Co-Fe-Sb ternary systems

Some primary crystalline phases of the Co-Ni-Sb and the Co-Fe-Sb systems are studied on the basis of the crystalline structure analysis by X-ray diffraction (XRD), the microstructure observation by scanning electron microscopy (SEM), the composition determination by electron probe microanalysis (EPMA) and the phase equilibrium relations of the constituent binary systems. From the experimental measurements of the present work and the phase equilibrium relations of literature reports, the liquidus projections of the Co-Ni-Sb and the Co-Fe-Sb ternary systems are determined. There exist 6 primary crystalline phases in each of the ternary systems, which are γ(A1)-Fcc_A1, β(Co,Ni)₃Sb-D0₃, γ(Co,Ni)Sb-NiAs, ζ(Co,Ni)Sb₂-FeS₂, η(Co,Ni)Sb₃-CoAs₃ and Sb-Rhombo_A7 in the Co-Ni-Sb system and γ(A1)-Fcc_A1, α(A2)-Bcc_A2, γ(Co,Fe)Sb-NiAs, ζ(Co,Fe)Sb₂-FeS₂, η(Co,Fe)Sb₃-CoAs₃ and Sb-Rhombo_A7 in the Co-Fe-Sb system. Two of invariant reactions are proposed, which are the eutectic reaction L → γ(A1) + β(Co,Ni)₃Sb + γ(Co,Ni)Sb in the Co-Ni rich side of the Co-Ni-Sb system and the transition reaction L + γ(A1) → α(A2) + γ(Co,Fe)Sb in the Co-Fe rich side of the Co-Fe-Sb system.     

Determination of the liquidus of the ternary system Cu-Sn-Ti

The liquidus surface of the ternary system Cu-Sn-Ti was established by determining the primary crystallizing phases as well as the phase reactions involving the liquid phase. The τ ₁CuSn₃Ti₅ and Ti₆Sn₅ have a wide field in terms of the primary composition. The primary crystallization of the τ ₂CuSnTi phase was observed in alloys containing 26 or more at.% Sn and up to 10 at.% Ti. In the tin-rich corner, the liquid phase solidifies in a ternary eutectic reaction.     

Determination of the liquidus of the ternary system Cu-Sn-Ti

The liquidus surface of the ternary system Cu-Sn-Ti was established by determining the primary crystallizing phases as well as the phase reactions involving the liquid phase. The τ ₁CuSn₃Ti₅ and Ti₆Sn₅ have a wide field in terms of the primary composition. The primary crystallization of the τ ₂CuSnTi phase was observed in alloys containing 26 or more at.% Sn and up to 10 at.% Ti. In the tin-rich corner, the liquid phase solidifies in a ternary eutectic reaction.     

Phase relationships in the Al-rich region of the Al-Cu-Er system

The Al-rich region of the ternary Al-Cu-Er system is investigated using the method of X-ray diffraction, scanning electron microscopy with energy dispersive X-ray spectroscopy. Phase equilibria in the Al-rich region of the Al-Cu-Er system at 673 K have been obtained, and the microstructures of as-cast alloys in the Al-rich region are also investigated. One ternary phase τ₁-Al₈Cu₄Er with a composition of 59.4-60.4 at.% Al, 32.2-33.8 at.% Cu, and 6.4-7.7 at.% Er is observed in both as-cast and annealed alloys. At 673 K, the binary Al₃Er phase dissolves about 3.51 at.% Cu. The calculated solidification paths (based on the CALPHAD method) of as-cast alloys are in agreement with the experimental results.     

Thermodynamic evaluation of hypereutectic Al–Si (A390) alloy with addition of Mg

This paper presents the thermodynamic evaluation of A390 hypereutectic Al–Si alloy (Al–17% Si–4.5% Cu–0.5% Mg) and alloys up to 10% Mg, using the Factsage® software. Two critical compositions were detected at 4.2% and 7.2% Mg where the temperatures of the liquidus, the start of the binary and of the ternary eutectic reaction are changed. These critical compositions show differences in the formation of Mg₂Si intermetallic particles during the solidification interval. For compositions up to 4.2% Mg, the Mg₂Si intermetallic phase first appears in the ternary eutectic zone. With Mg contents between 4.2% and 7.2%, Mg₂Si particle appears in both the binary and ternary eutectic reactions. Above 7.2% Mg, it solidifies as a primary phase and also during the binary and ternary reactions. The calculated liquid fraction vs. temperature curves also showed a decrease of the eutectic formation temperature (knee point temperature) with the addition of Mg content up to 4.2% Mg. This temperature becomes almost constant up to 10% Mg. The calculation of eutectic formation temperature shows a good agreement with differential scanning calorimetry (DSC) tests.     

Phase Equilibrium in the Ni-Ti-Zr System at 800 °C

The isothermal Ni-Ti-Zr phase diagram at 800 °C was constructed by means of 50 equilibrated alloys. Electron microprobe analyses were used to determine the phase compositions and phase relationships. There is one ternary phase Ni(Ti,Zr)₂ formed in the central region. Most of the Ni-Ti and Ni-Zr binary intermetallic phases show a large Zr or Ti solubility and extend to the ternary region. According to the results of DTA measurements, there are lower liquidus regions around the ternary phase due to the ternary phase reactions with the binary intermetallic phases. There is a potential region to form the bulk metallic glass.     

Microstructural characterization of Mo–12Si–8.5B alloy subjected to diffusion annealing treatment

Microstructural evolutions in the solidification and subsequent diffusion annealing treatment of Mo–12Si–8.5B alloys have been studied by using XRD, OM, SEM and TEM. Because the annealing temperature (1900 °C) is in the vicinity of four-phase equilibrium eutectic reaction (1950 °C) point of L = Mo₃Si + Mo₅SiB₂ (T₂)+Mo_ss (Mo solid solution), the dendrites and lamellar phase have almost been dissolved. Dislocations, Mo_ss precipitates and subgrain boundary have been observed in the T₂ phase while the other phases are not found. In addition, dislocations are from excess vacancy during the annealing treatment and play important roles for the Mo_ss precipitate. The dislocations can serve as the heterogeneous nucleation sites and compose of sub-boundary which refines the grain size to some extent. The results observed in this study can be used as a reference for future work on the relationships between microstructure and mechanical property of the Mo–Si–B alloys.     

Experimental thermodynamic study of intermetallic phases in the binary Ag–Te system by an improved EMF method

A thermodynamic study of the solid two-phase regions of the binary Ag–Te system was made by an improved EMF method, using fast ion conductor RbAg₄I₅ as the solid electrolyte. The EMF measurements were made on three galvanic cells: [Ag | RbAg₄I₅ | Ag₅Te₃ + Te], [Ag | RbAg₄I₅ | Ag₅Te₃ + Ag_1.9Te] and [Ag | RbAg₄I₅ | Ag_1.9Te + Ag₂Te].Based on the results obtained, the EMF for each equilibrium phase assembly was expressed as a function of temperature, in the different regions of thermal stability of the substances. By using the observed EMF and temperature relations, the thermodynamic functions of the stoichiometric equilibrium phase assemblages: Ag₅Te₃–Te, Ag₅Te₃–Ag_1.9Te, Ag₅Te₃–Ag₂Te and Ag₂Te–Ag_1.9Te, in the low-temperature range 22–204 °C, as well as phase transformation temperatures, have been determined. Agreement between the results obtained and the literature values were established.     

Isothermal section of the Ag2S-PbS-GeS2 system at 300 K and the crystal structure of Ag2PbGeS4

The isothermal section of the Ag₂S-PbS-GeS₂ system at room temperature was investigated by XRD. The existence of two quaternary compounds, Ag₂PbGeS₄ and Ag_0.5Pb_1.75GeS₄, was confirmed, and the phase equilibria between the binary system components and the ternary and the quaternary compounds were determined. The crystal structure of Ag₂PbGeS₄ was studied using the single crystal X-ray diffraction. It was established that Ag₂PbGeS₄ crystallizes in an own structural type in non-centrosymmetric space group Ama2 with the lattice parameters a = 1.02390(4) nm, b = 1.02587(5) nm, c = 0.67701(3) nm.     

The ternary Gd-Li-Mg system: Phase diagram study and computational evaluation

The binary Gd-Li and the ternary Gd-Li-Mg systems were studied experimentally by thermal analysis and phase equilibration and also by thermodynamic calculations using the CALPHAD method. Ternary phase equilibria at 250 °C were studied with 55 different alloys that were annealed for 400 h and analyzed by x-ray diffractometry. A thermodynamic assessment of the binary Gd-Li system was also performed and the calculated phase diagram is presented. In the Gd-Li-Mg system, ternary solubilities of Li in GdMg (up to 5 at.% Li), GdMg₂ (up to approximately 3 at.% Li), and GdMg₃ (up to 5 at.% Li) were found at 250 °C. No ternary compound was observed. Lattice parameters for different compositions are given for these phases. Thermal analysis using a ternary key sample of composition near the invariant reaction L′=L+(βGd)+GdMg provided the data that were needed to determine a thermodynamic parameter for the ternary liquid. Thermodynamic data sets for the ternary solid solution phases were also developed. Based on the present data sets and those of the binary Gd-Mg and Li-Mg systems from the literature, the phase equilibria in the entire ternary system were calculated. Isothermal and vertical sections of the phase diagram and the projection of the liquidus surface are shown. These calculated phase diagrams are well supported by the experimental data.     

Experimental Liquidus Surface Projection of the Ni-Ru-Zr System

SEM with EDX and XRD analyses were used to study 21 as-cast Ni-Ru-Zr alloys. Phases were distinguished by BSE image contrast, and the primary phases were determined by their dendritic morphology, with the solidification sequences derived from the microstructure. Identification of the phases was done by EDX analyses, and they were verified by XRD. From these analyses, the solidus and liquidus surface projections were drawn. Three ternary phases were found: τ₁ of composition ~Zr₂₄Ru₂₂Ni₄₄ (at.%), τ₂ at ~Zr₇₄Ru₄Ni₂₂ (at.%), and τ₃ at ~Zr₃₅Ru₃Ni₆₂ (at.%). Sixteen invariant reactions were identified, and the largest liquidus surface was for ~ZrRu.     

The ternary Gd-Li-Mg system: Phase diagram study and computational evaluation

The binary Gd-Li and the ternary Gd-Li-Mg systems were studied experimentally by thermal analysis and phase equilibration and also by thermodynamic calculations using the CALPHAD method. Ternary phase equilibria at 250 °C were studied with 55 different alloys that were annealed for 400 h and analyzed by x-ray diffractometry. A thermodynamic assessment of the binary Gd-Li system was also performed and the calculated phase diagram is presented. In the Gd-Li-Mg system, ternary solubilities of Li in GdMg (up to 5 at.% Li), GdMg₂ (up to approximately 3 at.% Li), and GdMg₃ (up to 5 at.% Li) were found at 250 °C. No ternary compound was observed. Lattice parameters for different compositions are given for these phases. Thermal analysis using a ternary key sample of composition near the invariant reaction L′=L+(βGd)+GdMg provided the data that were needed to determine a thermodynamic parameter for the ternary liquid. Thermodynamic data sets for the ternary solid solution phases were also developed. Based on the present data sets and those of the binary Gd-Mg and Li-Mg systems from the literature, the phase equilibria in the entire ternary system were calculated. Isothermal and vertical sections of the phase diagram and the projection of the liquidus surface are shown. These calculated phase diagrams are well supported by the experimental data.     

Reactive synthesis and mechanical properties of Mo2NiB2 based hard alloy

Using three elementary substances, Mo, Ni, and amorphous B powders as raw materials, the ternary boride based hard alloy Mo₂NiB₂–Ni was prepared successfully. The formation mechanism of the ternary phase was verified by XRD. It was indicated that the formed Mo₂NiB₂ particles at lower temperatures could be as seeds for the further formation of Mo₂NiB₂ directly from the raw materials of Mo, Ni and B at higher temperatures. The appearance of liquid phases between 1100 and 1200 °C was important for the densification of hard alloy. The microstructures of the hard alloys were observed by SEM. The main fracture modes for the hard alloys were different for the samples sintered at different temperatures. The maximum bending strength and the Rockwell hardness reached 1.85 ± 0.04 GPa and 85.7 ± 0.1 HRA, respectively. These values were comparable to those reported in literature.