Journal of Phase Equilibria and Diffusion最新文献

In this study, the phase equilibria of the Nb-V-Hf ternary system at 1300, 1100 and 1000 °C were experimentally investigated by means of back-scattered electron imaging, electron probe microanalysis, and x-ray diffraction. The results show that one ternary Laves compound with a hexagonal C14 structure is found in the isothermal sections that were studied. The bcc phase forms a large continuous solid solution, and no phase separation occurs at 1000 °C as had been claimed in the literature. As the temperature rises from 1000 to 1300 °C, the bcc structure can be observed in the Hf-V side, and the phase region of C15 reduces.

The solubility values of eight common alloying elements Al, Ca, Ce, Gd, Nd, Sn, Y and Zn in hcp Mg are experimentally measured from diffusion profiles obtained from diffusion multiples and liquid-solid diffusion couples (LSDCs) using electron probe microanalysis. These solubility values are used to stablish solidus and solvus lines and compared with the experimental results reported in the literature as well as the computed phase boundaries using two CALPHAD (CALculation of PHAse Diagrams) databases. Our experimental values for Mg-Ca (530, 580, 600, 630 °C), Mg-Ce (605, 630 °C), Mg-Gd (570, 600, 630 °C) and Mg-Nd (615, 630 °C) are the first ever measurements of the hcp solidus for these four binary systems. Additional solubility data obtained from our experiments are reported for Mg-Al (375, 420, 450, 500, 550, 600 °C), Mg-Sn (375, 420, 500, 550, 600 °C), Mg-Y (590, 610, 630 °C), and Mg-Zn (275, 450, 500, 550 °C). Our experimental data are valuable input to future thermodynamic reassessments of the eight binary systems. This study also clearly shows the effectiveness of measuring solidus data using the elegant LSDCs.

The LiCl-KCl-GdCl₃ quasi-ternary phase diagram has been investigated by differential thermal analysis (DTA) and x-ray diffraction (XRD) techniques. These experiments showed that the LiCl-KCl-GdCl₃ system consists of several pseudo-ternary and quasi-ternary composition triangles. Coexisting phases in the solid state at 260 °C were characterised by XRD analysis of the equilibrated samples. Quasi-ternary compounds were not found. The ternary eutectic temperature was observed at 315 ± 2 °C and its composition was delineated at 57 mol.% LiCl-42 mol.% KCl-1 mol.% GdCl₃ in the LiCl-KCl-K₃GdCl₆ composition triangle. The other ternary eutectic temperature was observed at 308 ± 2 °C in the LiCl-K₃GdCl₆-K₂GdCl₅ composition triangle. Its composition was deduced at 40.2 mol.% LiCl-41.7 mol.% KCl18.1 mol.% GdCl₃. Another ternary eutectic temperature was observed at 360 ± 9 °C in the LiCl-K₂GdCl₅-KGd₂Cl₇ composition triangle. Its composition was deduced at 33.8 mol.% LiCl-29.5 mol.% KCl-36.7 mol.% GdCl₃. The fourth ternary eutectic temperature was observed at 362 ± 4 °C in the LiCl-KGd₂Cl₇-LiGdCl₄ composition triangle. Its composition was delineated at 48 mol.% LiCl-11 mol.% KCl-41 mol.% GdCl₃. The ternary pseudo-peritectic reaction “L+GdCl₃ ↔ LiGdCl₄+KGd₂Cl₇” was observed at 370 ± 3 °C. Its composition was delineated at 46.7 mol.% LiCl-10.5 mol.% KCl-42.8 mol.% GdCl₃. The primary and secondary crystallisation temperatures, as well as polymorphic phase transformation temperatures of the samples were deduced from the heating runs of DTA experiments. Further, phases responsible for the various thermal events were ascertained. Isothermal composition triangles at selected temperatures, Scheil diagram and the polythermal liquidus projection with isothermal contours of the ternary phase field were drawn.

Phase equilibria in Ga-Sn-Te system plays a key role in designing multiphase thermoelectric materials. SnTe is a promising alternative to the well-known PbTe (toxic) thermoelectric phase in the Ga-Sn-Te system. In the present study, various compositions have been selected using the thermodynamically developed database of the Ga-Sn-Te system to understand the phase equilibria and microstructural features. The alloys with multiphase combinations of SnTe, Ga₆SnTe₁₀, GaTe, and Te were produced using vacuum induction melting. In addition, the developed microstructures were characterized using x-ray diffraction, optical and Scanning Electron Microscopy techniques. The microstructures reveal interesting eutectic morphologies of Ga₆SnTe₁₀/Te, Ga₆SnTe₁₀/SnTe, and GaTe/SnTe. The microstructural features were explained using Scheil-Gulliver cooling calculations. Moreover, the thermal analysis of the investigated alloys was also performed to validate the thermodynamically predicted liquidus temperatures and various phase transitions in the investigated alloys.

The equilibrium phase relations of the Nd₂O₃-CaO-Fe₂O₃ system were investigated at 1473 K in air using a high-temperature isothermal equilibration technique followed by quenching. Using x-ray diffraction (XRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS) analysis of quenched samples, twelve two-phase equilibria regions and eleven three-phase equilibria regions were observed. A series of solid solutions Nd_1−xCa_xFeO_3−δ formed in the ranges of 0 ≤ x ≤ 0.2, 0.5 ≤ x ≤ 0.6, and 0.6 < x ≤ 1 were found. Ternary compound Ca_1−xNd_1+xFeO_4−δ was observed to be stable at 1473 K with limited substitution of Nd by Ca. The 1473 K isothermal section was constructed for the Nd₂O₃-CaO-Fe₂O₃ system.

There is an increasing demand for materials capable of withstanding ever-higher temperatures. However, because the difficulties associated with carrying out experimental investigations at very high temperatures are significant, the published information relating to the phase stability of potential refractory materials is, in many instances, still lacking. The work described in this paper attempts to rectify this deficit through the on-going development of a thermodynamic database for high-temperature materials based on carbides, nitrides, borides, and silicides. Because of technological requirements of high-temperature stability and strength, combined with lightness, these are the materials that come into question most frequently for high-temperature applications. In developing the present database, and to ensure reliability of its use, emphasis has been placed on the need to maintain the compatibility of data and modeling when assessing experimental data and estimating missing values. The methods used to achieve compatibility of published information are described and calculations of phase equilibria relevant to the industrial application of various refractory materials are presented. The similarity to, and the importance of the scientific background and published work of Ted Massalski for the work of the present author is stressed.

Phase equilibria in the Zr-Ti-Cu system have been studied by differential thermal analysis, scanning electron microscopy, x-ray microanalysis, and x-ray diffraction. Based on the obtained results, a ternary phase diagram was constructed over the entire composition range in the crystallization interval. The results are presented in the form of liquidus and solidus projections, the Scheil reaction scheme, and isopleths for sections of 40 and 70 at.% Cu. Phase equilibria in the system are defined by the ternary compound ZrTiCu₂ (τ₁) and the binary-based phase Zr₁₄Cu₅₁. These phases have the widest fields of primary crystallization on the liquidus projection and form two-phase equilibria with all other phases on the solidus projection. The solidus projection contains 11 three-phase fields. Two of them form by invariant four-phase reactions of the transition type, the rest by eutectic ones. A comparison of the solidus projection with the published isothermal sections at 800 and 750 °C led to the need for two solid-state four-phase invariant equilibria involving binary Ti-Cu intermetallic compounds. They are shown to occur between 840 and 850 °C. The ternary compound Zr₂₂Ti_14.5Cu_63.5 (τ₂) was shown to form in the solid state at 827 °C by three-phase invariant reaction τ₁ + Zr₁₄Cu₅₁ ⇄ τ₂.

Thermodynamic properties of titanium are evaluated to 3700 K. Selected values include an enthalpy of sublimation value of 472.6 ± 1.0 kJ/mol at 298.15 K and a boiling point at one atmosphere pressure of 3618 K.

Phase equilibria were investigated between 200 and 800 °C in the Cu-Zn binary system. Wavelength dispersive spectroscopy (WDS) was performed to determine the equilibrium compositions, and differential scanning calorimetry (DSC) was performed to investigate the solidus and liquidus temperatures and the invariant reaction temperatures of the Zn-rich portion. The β/(α + β) boundary in the Cu-rich portion extended toward the Cu-rich side as the temperature decreased below the A2–B2 order–disorder transformation temperature, and the phase boundaries of the γ, δ and ε phases shifted toward the Cu-rich side. The liquidus temperatures of the ε + liquid were higher than those of the previous report. From the experimental results, the phase diagram of the Cu-Zn binary system was determined in the whole composition range.