Journal of Phase Equilibria and Diffusion最新文献

Hillert often used the combined first and second law of thermodynamics to discuss and derive the principles of equilibrium as well as non-equilibrium thermodynamics. His method will now be reviewed and applied to reactions in homogeneous systems as well as transport processes As an example of homogeneous systems undercooled liquids and glasses is discussed.

Two methods were used to investigate the Y₂O₃-Ta₂O₅ system: the equilibration method, which covered temperatures from 1573 to 1973 K, and the DTA method, which reached up to 2473 K. Phase identification was carried out using x-ray diffraction and scanning electron microscopy with energy-dispersive x-ray spectroscopy (SEM/EDX). The temperature of the eutectic reaction, L → YTa₃O₉ (P) + Ta₂O₅, was determined to be 2019 K, with the corresponding eutectic composition being 78 mol.% Ta₂O₅. The study presents evidence that contradicts the existence of the eutectic reaction L → YTaO₄ (T) + YTa₃O₉ (P). Instead, it identifies a peritectic reaction L + YTaO₄ (T) → YTa₃O₉ (P), which was observed at a temperature of around 2075 K. Additionally, the heat capacity of the YTa₃O₉ (P) phase was measured using differential scanning calorimetry (DSC) over the temperature range from 240 to 1300 K. The results of this experimental investigation will lead to the development of a thermodynamic database for the Y₂O₃-Ta₂O₅ system.

Nickel-base superalloys contain high amounts of solutes like Cr, Mo, W, Nb, Ti, etc. These solutes promote the formation of different types of carbide and boride phases that may contain multiple elements. Researchers have mostly discussed the roles of primary elements responsible for the formation of a given carbide/boride phase, often ignoring the role of other solutes on its stability. In the present work, thermodynamic stability of carbide and boride phases in seven commercial superalloys, namely, Alloy 625, Alloy 690, Alloy 718, MAR M246, Rene 100, Udimet 710 and Nimonic 80A, has been studied using the CALPHAD based Thermo-Calc software. The aim of the study was to understand the role of different alloying elements on temperature stability and chemical compositions of equilibrium phases in superalloys. As the accuracy of CALPHAD based predictions depends upon the database used, a detailed examination of its inadequacies has also been carried out to ascertain the limitations of the predicted data. From the calculated equilibrium chemical compositions, major and minor constituents promoting the formation of carbides and borides have been identified. The individual effect of a given solute as well as the synergistic effect of two solutes on the relative thermodynamic stability of carbide/boride phases has been identified using property diagrams and isothermal sections of the temperature-composition diagrams. Most of the simulated results have been found to be consistent with the experimental data available in the literature. From a comparison of the experimental literature and the simulated data of the stable carbide and boride phases in the studied alloys, the interplay of different solutes has been deduced to define conditions under which these phases form, within the limitations of the database used. This study has helped in better understanding of general tendencies of solutes to form different carbide and boride phases in nickel-based superalloys.

Improving the oxygen diffusion capacity of solid electrolyte material is an important goal of researchers in recent decades. For this purpose, the blackening of zirconia was considered as a new strategy to enhance its oxygen diffusion capacity. We comparatively investigated the oxygen transport properties of white (YSZ, yttria stabilized zirconia) and black (ZSZ, Zr³⁺ stabilized zirconia) zirconia by molecular dynamics simulation. The simulation results show that the ZSZ has the same oxygen diffusion mechanism as YSZ. Furthermore, the ZSZ has a much better oxygen diffusion capacity than YSZ, which is confirmed by the lower minimum oxygen diffusion activation energy of ZSZ (0.37 eV) than that of YSZ (0.46 eV). The different oxygen diffusion capacity between YSZ and ZSZ is attributed to their crystal structure difference. The Zr³⁺ ionic radius is much closer to that of Zr⁴⁺ than that of Y³⁺, and it induces smaller lattice distortion in stabilized zirconia to impose a minimal steric blocking effect on the oxygen diffusion process. Therefore, the Zr³⁺ is preferred over Y³⁺to enhance the oxygen diffusion capacity of stabilized zirconia and the black YSZ co-doped by Y³⁺ and Zr³⁺ is proven to be a promising solid electrolyte material with a better oxygen diffusion capacity than YSZ.

In this work, the phase equilibria of the binary Ag-In system were determined using electron probe microanalysis and differential scanning calorimetry on equilibrated alloys and diffusion couples. The compositions of the phase boundaries of solid phases that are highly scattered in the literature have been precisely determined. The temperatures of the invariant reaction ζ ⇄ γ + L and the polymorphic transformation ζ ⇄ γ are substantially lower than previously reported values. In addition, it was found that the In-rich ζ phase phase-separates after months of room-temperature aging.

Multicomponent phase space has been shown to consist of an enormous number of materials with different compositions, the vast majority of which have never been made or investigated, with great potential, therefore, for the discovery of exciting new materials with valuable properties. At the same time, however, the enormous size of multicomponent phase space makes it far from straightforward to identify suitable strategies for exploring the plethora of potential material compositions and difficult, therefore, to be successful in discovering desirable new materials. Unfortunately, all our knowhow and understanding has been developed for materials with relatively few components in relatively limited proportions, with most of our scientific theories relying essentially on linear assumptions of component dilution and independence that no longer apply in concentrated multicomponent materials. Trial and error, controlled substitution, parameterisation, thermodynamic modelling, atomistic modelling and machine learning techniques have all been employed as methods of exploring multicomponent phase space, with varying levels of success, but ultimately none of these techniques has proved capable of delivering consistent or guaranteed results. This paper provides an overview of the different techniques that have been used to explore multicomponent phase space, indicates their main advantages and disadvantages, and describes some of their successes and failures.

The phase equilibria of the Er-Al-Zr ternary system at 500 °C were investigated using a combination of electron probe microanalyzer and x-ray diffraction. The microstructure and diffraction peaks were analyzed to determine the phases and compositions of Er-Al-Zr ternary system. Based on the experimental results, the isothermal phase diagram of the Er-Al-Zr ternary system consists of 14 three-phase equilibrium regions, 15 two-phase equilibrium regions, and 13 stable binary compounds, but no ternary compounds were detected. The solubility of Er in the Al₂Zr, Al₃Zr₂, AlZr, Al₃Zr_4, Al₂Zr₃ is 9.9, 5.3, 9.0, 12.4, 6.7 at.%, respectively. The present work could be important for alloy design of Al-based alloys and thermodynamic analysis of the Er-Al-Zr ternary system.