Calculated Phase Diagram Research Articles

Enhancing growth speed of 3C–SiC using solution growth method by a new low temperature Mn-based cosolvent

Solution growth is a promising method for rapidly and stably preparing high-quality silicon carbide (SiC) single crystals. However, the coexistence of polycrystalline parasitism and solid inclusions during the growth of SiC in high-temperature solutions above 1800 °C still poses a serious threat to the quality of single crystals. Herein, we introduce an innovative Mn-based cosolvent for controlling the stable and fast growth of cubic-type silicon carbide (3C–SiC) single crystals at low temperatures. Firstly, our thermodynamic analysis reveals that SiC is the only stable solid compound in the low-temperature solution (1500–1600 °C) of the Si–Mn–C system, which is an important condition for the stable growth of crystals. Compared to typical solvents like Si–Cr, Si–Ti, and Si–Fe, the Si–Mn solvent exhibits the highest solubility and supersaturation for carbon. Secondly, our solubility calculations of SiC in the solvent show that the Mn-rich solvent can significantly increase the solubility of SiC. Thirdly, we successfully grew 3C–SiC single crystals from Si–Mn solution at 1500 °C without other SiC polymorphs produced. Rapid growth of SiC crystals in Mn-rich solution was achieved by modulating the content of Mn. Our work highlights the superiority of Si–Mn cosolvents in facilitating rapid growth of 3C–SiC single crystals at low temperatures. It introduces a novel approach by applying phase diagram calculation techniques to design suitable solvent systems for the solution growth of SiC single crystals.

Design and Selection of High Entropy Alloys for Hardmetal Matrix Applications Using a Coupled Machine Learning and Calculation of Phase Diagrams Methodology

This study aims to utilize a combined machine learning (ML) and CALculation of PHAse Diagrams (CALPHAD) methodology to design hardmetal matrix phases for metal‐forming applications that can serve as the basis for carbide reinforcement. The vast compositional space that high entropy alloys (HEAs) occupy offers a promising avenue to satisfy the application design criteria of wear resistance and ductility. To efficiently explore this space, random forest ML models are constructed and trained from publicly available experimental HEA databases to make phase constitution and hardness predictions. Interrogation of the ML models constructed reveals accuracies >78.7% and a mean absolute error of 66.1 HV for phase and hardness predictions respectively. Six promising alloy compositions, extracted from the ML predictions and CALPHAD calculations, are experimentally fabricated and tested. The hardness predictions are found to be systematically under‐ and overpredicted depending on the alloy microstructure. In parallel, the phase classification models are found to lack sensitivity toward additional intermetallic phase formation. Despite the discrepancies identified between ML and experimental results, the fabricated compositions show promise for further experimental evaluation. These discrepancies are believed to be directly associated with the available databases but, importantly, have highlighted several avenues for both ML and database development.

Thermodynamic optimization of KCl-LiCl-LaCl3 with ionic two-sublattice model for liquid

The pyroprocessing technology can reduce nuclear waste by recovering uranium from spent nuclear fuels. To fully take advantage of this technique, it is crucial to have a better understanding of the thermodynamic behavior evolution of the eutectic KCl-LiCl electrolyte with the accumulation of impurities such as lanthanides. The present study carries out thermodynamic modeling for the KCl-LiCl-LaCl3 system and its binary subsystems using the CALPHAD (CALculation of PHAse Diagrams) approach for the first time to predict the liquidus temperatures of KCl-LiCl eutectic as a function of LaCl3 content. Three possible ionic two-sublattice models have been implemented to describe the liquid phase for comparison. Model 1 only involves simple cations and anions. Model 2 and 3 consider short-range ordering in the liquid and introduce species K2LaCl5 and LaCl63-, respectively. It was demonstrated that from the thermodynamics point of view, Model 1 is sufficient to reproduce both phase equilibria and enthalpy of mixing data, whereas Models 2 and 3 seem redundant and increase the number of parameters, which may further lead to poor extrapolation behavior towards multicomponent systems. To achieve better agreements with experimental phase equilibria data and estimated enthalpy of mixing data using the surrounded-ion model, three ternary parameters were optimized for the KCl-LiCl-LaCl3 system. The resultant calculations can well reproduce the experiments and provide insights into the liquidus temperature variation as the mole fraction of LaCl3 increases in the electrolyte.

An improved method for the quantification of microstructures via optical microscopy

Quantitative optical microscopy is a powerful tool for microstructural characterization of relatively large areas of multiphase materials, but accurate quantification often requires skillful sample preparation, imaging, and analysis techniques. Measuring phase fractions in a microstructure is done by segmenting images between features of interest and everything else and can be accomplished by a variety of techniques. With existing methods, in many cases, optimal contrast between the features of interest and the surrounding microstructural constituents is difficult to obtain and inconsistent across both individual images and a sample surface due to normal variations in materials and equipment, which can introduce measurement errors. A new machine-learning tool, the Labkit ImageJ plugin, provides a user-friendly method for training models for quantitative metallography and can be generally applied to study a wide variety of multiphase materials. Sørensen–Dice Indices were calculated to provide accuracy metric and show the improvement in image segmentation using Labkit to other common contrast-based thresholding methods versus manually-segmented representative images throughout the temperature range of this study. An example using intercritically heat treated HY-80 steel containing a duplex microstructure is presented using three different optical microscopy quantitative methods to show the improvement in reliability from the Labkit plugin. These quantitative measurements are augmented by differential scanning calorimetry and compared to CALculation of PHAse Diagram (CALPHAD) models to highlight the importance of experimental data for the design of heat treatments. A method for calibrating CALPHAD models to better predict industrial heat treatments is presented and shown to improve the accuracy of phase-fraction predictions, which is crucial for execution of intercritical heat treatments of steels.

The Beneficial Effect of Iron in Aluminum-Cerium-Based Cast Alloys

Iron (Fe) has been considered a major impurity since it is detrimental to the mechanical properties of many cast aluminum alloys due to the formation of Fe-containing brittle intermetallic phases. Fe is found naturally as an impurity in bauxite ore, resulting in Fe contamination of aluminum alloys with increasing contamination from current recycling practices. The Al–Ce–Fe system was investigated using CALPHAD (CALculation of PHAse Diagrams) modeling and experimental casting techniques. It was found that additions of Fe to the Al–Ce system are beneficial to the strength (slightly) and ductility (significantly) of the ternary alloys, which is attributed to the formation of fine metastable Al8CeFe2 phase with aggregate morphology and equilibrium Al10CeFe2 phase, suppressing coarse proeutectic Al11Ce3 phase in near-eutectic Al–Ce alloys. Heat treatment study showed that the metastable Al8CeFe2 phase transforms to predicted equilibrium Al10CeFe2 phase at 500 °C, with essentially no intermetallic or grain coarsening; thus, the alloy displayed excellent property retention. The Al–Ce–Fe alloy system offers opportunities for sustainable, recyclable alloy development using low-cost Fe and low-cost cerium (a byproduct of rare-earth extraction).

Exploring NiCrAlYSiTa multicomponent coatings: Combining high-throughput synthesis and CALPHAD modeling

Multicomponent alloys pose great challenges for efficiently screening desired composition. Here, we combined high-throughput magnetron-sputtering experiments and CALculation of PHAse Diagrams (CALPHAD) methods to screen NiCrAlYSiTa coatings. The compositionally graded coatings showed increased amorphization with higher Si content, indicated by the steepen T0 curves and enlarged amorphous formation region. For the crystallized coatings, the phase structure transformed from Al- and Cr-rich bcc region to Ni-rich fcc, consistent with our calculated phase diagrams. Owing to the high cohesion energy and strong atomic bonding induced by large atomic radius difference and negative mixing enthalpy, the amorphous coatings exhibited superior hardness (25.8 GPa) and elastic modulus (415.8 GPa) compared to the reported multicomponent coatings. By combining high-throughput experimental and theoretical methods, this work pioneers an integrated framework for rapid development of new multicomponent alloy coatings.

Solid-liquid phase equilibria of quaternary systems LiCl+KCl+NaCl+H2O and LiCl+KCl+MgCl2+H2O at 308.2K

The phase equilibria of quaternary systems LiCl+KCl+NaCl+H2O and LiCl+KCl+MgCl2+H2O at 308.2 K were investigated by isothermal dissolution equilibrium method. The results reveal that the phase diagram of the quaternary system LiCl+KCl+NaCl+H2O consists of one invariant point, three univariable curves and three equilibrium solid crystallization fields (LiCl·H2O, NaCl and KCl). Two double salts appear in the quaternary system LiCl+KCl+MgCl2+H2O, namely KCl·MgCl2·6H2O and LiCl·MgCl2·7H2O, and the phase diagram is composed of three invariant points, seven univariable curves and five crystallization fields (LiCl·MgCl2·7H2O, MgCl2·6H2O, LiCl·H2O, KCl and KCl·MgCl2·6H2O). Moreover, the solubilities of salts in two quaternary systems are predicted by applying the Pitzer model. The calculated phase diagrams were in good accordance with the experimental phase diagrams. The results clearly show that lithium chloride crystallizes as LiCl·2H2O at low temperatures; however, it is precipitated as LiCl·H2O at 308.2 K. Compared with KCl·MgCl2·6H2O, LiCl·MgCl2·7H2O has a smaller crystallization zone. The phase equilibria in invariant points of quaternary systems LiCl+KCl+NaCl+H2O and LiCl+KCl+MgCl2+H2O at 308.2 K have been explored for the first time.

Calculation of phase diagram and the thermodynamic quantities by the Landau mean field model close to the solid – liquid and solid – solid transitions in n-paraffins

ABSTRACT We calculate the phase diagrams and predict the temperature dependence of the thermodynamic quantities at high pressures for the solid – liquid and solid – solid transitions in n-paraffins. This calculation is performed by fitting the phase line equations as obtainedfrom the Landau model to the experimental data from the literature. On thebasis of the Landau model, phase diagram of the solid – solid transition ispredicted at 0.1 MPa for the binary mixtures of n-tridecane + (n-hexane and cyclohexane).For the calculation of the heat capacity the extended mean field is employedfor the n-paraffins studied here. We find that our calculated phase diagrams explain the observed behaviour of the liquid – solid transitions at high pressures in those binary mixtures. Our phase diagrams predicted at 0.1 MPa and our predictions for the thermodynamic quantities can be compared with the experiments for those binary mixtures.

Solute Effects on Growth Restriction in Dilute Ferrous Alloys

The effect of dilute solute additions on growth restriction in binary ferrous alloys has been assessed by means of the heuristic growth restriction parameter (β) modelling framework (Fan et al. in Acta Mater. 152, 248–257, 2018). The CALPHAD (CALculation of PHAse Diagrams) methodology (Kaufman and Bernstein in Computer Calculation of Phase Diagrams, 1970) has been used to calculate β values from the liquidus slope m and the equilibrium distribution coefficient k values, at first approximation, in conjunction with the liquid-to-solid fraction to obtain true β values. Critical solute concentrations, below which solidification becomes partitionless, have also been calculated. Among 23 dilute binary ferrous alloy systems investigated, the five most efficient solutes on grain refinement are B, Y, O, S and C. A negative correlation, or inverse relationship, was observed between the true β values and the grain size values obtained from a study on experimental multicomponent dilute ferrous alloy systems (Li et al. in Metall. Mater. Trans. A 49 A, 2235–2247, 2018).

Systematic Study on the Microstructures of Biomedical Co–20Cr–15W–10Ni Alloys with Carbon Contents Ranging from 0 to 0.2 mass pct

Herein, the effect of carbon content on the microstructures of Co–20Cr–15W–10Ni (mass pct, CCWN) alloys was systematically studied. For this, CCWN alloys with carbon contents of 0, 0.05, 0.10, and 0.20 mass pct, i.e., 0C, 0.05C, 0.10C, and 0.20C alloys, respectively, were prepared using an induction melting furnace. The as-cast alloys were solution treated at 1523 K for 7.2 ks, followed by cold swaging and heat treatment at 1173 K–1473 K for 0.15–7.2 ks. Consequently, η-phase (M6C-M12C type, M: metallic element) precipitates were detected in the as-cast 0.10C and 0.20C alloys, whereas no precipitates were observed in the 0C and 0.05C alloys. These precipitates were dissolved via a solution treatment. After cold swaging, the ε-phase formed through a strain-induced martensitic transformation in the 0C and 0.05C alloys. Following heat treatment, a single γ-phase matrix was observed in all the alloys, and μ-phase (Co7W6-type) and η-phase precipitates were observed in the 0C and carbon-added alloys, respectively. The precipitation temperature range of the η-phase increased with increasing carbon content. The stability of the precipitates qualitatively conformed with that of the calculated phase diagram. This is the first paper that reports the microstructural changes in CCWN alloys with varying carbon contents.

Application of CALPHAD Method for Predicting of Concentration Range of Amorphization of Transition Metals Melts

Early, the efficiency of the CALPHAD (Calculation of Phase Diagrams) method to a targeted search for compositions of amorphous alloys has been shown. The method for predicting the ranges of amorphization is based on the calculation of diagrams of metastable phase transformations between supercooled melts and boundary solid solutions on the base of pure elements. In this work, the model parameters for thermodynamic properties of liquid alloys and boundary solid solutions were summarized in a self-consistent database for the multicomponent Cu–Fe–Ni–Ti–Zr–Hf system. Such database for the multicomponent system is based on a common set of model parameters for boundary binary and ternary systems. This database was used to predict the concentration ranges of amorphization for the quinary Cu–Fe–Ni–Ti–Zr, Cu–Fe–Ni–Ti–Hf and boundary ternary and quaternary systems. The results of calculations are presented along sections in quaternary and quinary systems. The ternary and quaternary equiatomic alloys along with high entropy CuFeNiTiZr and CuFeNiTiHf alloys are trapped into prognosed composition ranges of amorphization. Predicted composition space of amorphization for melts of the Fe–Ni–Ti–Zr system is shown on the concentration tetrahedron. Based on the obtained results, a new criterion for predicting the concentration regions of amorphization of multicomponent melts is proposed, according to which the presence of a sufficient content of metals that are electron acceptors and donors is a chemical factor that affects the thermodynamic stability of melts and determines their glass-forming ability. For multicomponent melts of the Cu–Fe–Ni–Ti–Zr–Hf system the concentration ranges of amorphization correspond to the simultaneous fulfillment of the conditions xFe + xNi + xCu > 0.25 and xTi + xZr + xHf > 0.15, where Fe, Ni, and Cu are electron acceptors and Ti, Zr, and Hf are electron donors.

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In the present work, phase equilibria in the Li2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}O–Al2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}O3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document} system were experimentally studied and calorimetric measurements were performed. Based on obtained results and data from literature, thermodynamic parameters of the system were assessed. The solid solution phases were modeled using Compound Energy Formalism (CEF) and liquid phase was described by two-sublattice partially ionic liquid model. The experimental investigations for selected compositions of isothermally heat-treated samples were performed using x-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). Differential Thermal Analysis (DTA) and Differential Scanning Calorimetry (DSC) were used to measure the temperature of the reactions as well as the heat capacities, respectively. After DTA, the microstructure was analyzed using SEM. 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Heat capacity of LiAlO2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document} and LiAl5\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_5$$\\end{document}O8\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_8$$\\end{document} was measured in the temperature range of 100-1300 K. The degree of inversion of spinel phase (Al+3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{+3}$$\\end{document}, Li+1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{+1}$$\\end{document})1T\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_1^T$$\\end{document}:(Al+3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{+3}$$\\end{document}, Li+1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{+1}$$\\end{document}, Va)2O\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2^O$$\\end{document}:O4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document} was modelled assuming Al+3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{+3}$$\\end{document} and Li+1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{+1}$$\\end{document} can occupy tetrahedral (T) and octahedral (O) cationic sublattices while its composition extension in Al2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}O3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_3$$\\end{document} enriched region was described by introducing vacancies in octahedral sites. Thermodynamic description derived in the present study reproduces the degree of inversion close to that of the high-temperature spinel phase, which means that Al+3\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{+3}$$\\end{document} ions preferentially occupy the tetrahedral sites. The calculated phase diagram satisfactorily agrees with the experimental results. Available experimental thermodynamic data are also reproduced within uncertainty limits.

Chlorine Solubility in Silicate Melts: New Experiments and Thermodynamic Mixing Model

We present new experimental data on Cl solubility in model basalt melts of eutectic compositions diopside (Di)–albite (Ab) and Di–anorthite ± quartz (Qtz). The starting glasses were equilibrated with aqueous NaCl–CaCl2 fluid at 4 kbar in the temperature range of 900–1200°C. The experiments show that Cl solubility decreases with increasing NaCl in the fluid. Ca–Na partitioning between melts and fluid is weekly temperature dependent and resembles that of the plagioclase–fluid system. The newly obtained experimental data, along with previously published results on the model granite melting in the presence of (Na,K)Cl brines (Aranovich et al., 2013), are used to calibrate an empirical thermodynamic model for salt species (NaCl, KCl, and CaCl2) in silicate melt. Calculations show that Cl solubility in haplogranite melt decreases with increasing K/Na ratio in the fluid (and correspondingly, melt). The data acquired on Ca and Na partitioning between melt and fluid make it possible to model the evolution of the Ca/Na ratio in the crystallization course of basalt melts. At a high pressure (10 kbar), Cl solubility in model granite increases with increasing Н2О content. The calculated phase diagram for a simple pseudo-ternary system Ab–H2O–NaCl demonstrates complex phase relations and, correspondingly, evolution of the Н2О and NaCl concentrations in the melt. This complex evolution is illustrated by data on the composition of quartz-hosted melt and fluid inclusions from granites in the Verkhneurmisskii massif in the Badzhal volcano-plutonic zone.

High-Pressure Die Casting of Al–Ce–La–Ni–Fe Alloys

The effects on phase equilibria of La and Fe additions to the Al–Ce–Ni-based alloy system are explored under high-pressure die casting conditions. The addition of La to Al–Ce–Ni-based alloy system only reacts with Ce synergistically to promote the formation of the Al11(Ce,La)3 intermetallic phase as predicted by CALculation of PHAse Diagrams (CALPHAD) and verified experimentally. High Fe additions react with Ni to form the Al9FeNi intermetallic phase, which is an additional eutectic former. The targeted co-precipitation type eutectic morphology is achieved in the alloys studied. Additional coarse particles of Al11(Ce,La)3, present in the alloys studied and not predicted by CALPHAD, are attributed to possible inclusions of Ce and La oxide, present in the mischmetal feedstock used. Both alloys exhibit exceptional mechanical stability after 10 hours at 400 °C due to the stability of the phases formed during solidification. The alloy with high Fe additions possessed better mechanical properties after heat treatment based on the higher eutectic content and more substantial improvement to the morphology of secondary phases after treatment.

Experimental investigation and thermodynamic assessment of phase equilibria in the Al–Cr–Ta ternary system

The Al–Cr–Ta ternary system was investigated through a combination of experiments and thermodynamic modeling. The determination of the liquidus projection involved the microstructural characterization of 29 as-cast alloys using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). Sublattice models were proposed for the phases according to their crystal structures and homogeneity ranges. Based on the experimental results, the Al–Cr–Ta ternary system was thermodynamically assessed by the CALculation of PHase Diagrams (CALPHAD) approach. The liquidus projection, isothermal sections, and vertical sections of the ternary system were calculated. A set of self-consistent thermodynamic parameters for the Al–Cr–Ta ternary system was obtained with a satisfactory agreement between the experimental and calculated results. The present work could be significant for the practical application of novel cemented carbides and future thermodynamics assessment of complex multicomponent systems.

Phase transitions, conductance fluctuations and distributions in disordered topological insulator stanene

It is essential to understand to what extent the protected edge states of topological insulators (TIs) can survive against the degradation of the ubiquitous disorders in realistic devices. From a different perspective, disorders can also help to enrich the applications by modulation of the phases in TIs. In this work, the phases and phase transitions in stanene, a two-dimensional TI, have been investigated via the statistical approach based on the random matrix theory. Using a tight binding model with Aderson disorder term and the Landauer–Büttiker formalism, we calculated the conductance of realistic stanene ribbons of tens of nanometers long with random disorders. The calculated phase diagram presents TI in the gap, metal in high energy and ordinary insulator in large disorder region. Increasing the width of the ribbon can significantly enhance the robustness of TI phase against disorders. Due to different underlying symmetries, the metallic phase can be further categorized into unitary and orthogonal classes according to the calculated universal conductance fluctuations. The local density of states is calculated, showing characteristic patterns, which can facilitate the experimental identification of the phases. It is found that different phases have distinguishing statistical distribution of conductance. Whereas at the phase boundary the distribution exhibits intermediate features to show where the phase transition occurs. To reveal the phase evolution process, we further studied the effects of the disorders on respective transmission channels. It is found that when phase transition takes place, the major transmission channels of the old phase are fading and the new channels of the new phase are emerging.

Corrosion resistance investigation of the Ti–Al–Mo system supported by CALPHAD approach and key experiments

The corrosion resistance of Ti–Al–Mo alloys in seawater were investigated by thermodynamic calculations and electrochemical tests. Four as-cast alloys were designed based on thermodynamic calculations. The calculated results were verified by experimental determination. The Gibbs energy and electrochemical experiment results showed Ti55Al40Mo5 alloy has the most positive Gibbs energy and the best corrosion resistance. The bcc(Ti) phase has best corrosion resistance among AlTi, AlTi3 and bcc(Ti). The present work further proves the important role of phase diagram calculation in alloy design, and thermodynamic database provides important theoretical support for efficient development of new alloys.

Computational thermodynamic study on CVD of silicon oxynitride films from Si–O–N–H and Si–O–N–H–Cl systems

High-throughput thermodynamic analysis of chemical vapor deposition of silicon oxynitride films from the Si–O–N–H and Si–O–N–H–Cl systems are performed based on the CALPHAD (CALculation of PHAse Diagram) approach. The considered deposition conditions are 800 °C, 200 Pa, NH3/SiH4 ratios of 0.05–50 and NH3/N2O ratios of 0.05–10. The influence of precursor composition on the phase and composition of the coatings as well as the optimal window for obtaining high-purity Si2N2O are discussed. The formation of SiO2 favors low NH3/N2O ratios and its fraction decreases with increasing NH3/N2O ratio. The content of Si2N2O increases monotonously with increasing NH3/N2O ratio until reaching 100 at.%. Free Si is suppressed to almost 0 at.% when the NH3/SiH4 ratio is greater than 1. The introduction of Cl in the precursor can not only reduce the formation of free Si but also expand the deposition window for preparing pure Si2N2O. Our calculated results agree well with available experimental data.

Development and directed energy deposition of high strength Hf5Mo15Nb35Ta25Ti20 refractory high entropy alloys

In this study, a novel HfMoNbTaTi refractory high entropy alloy was designed by empirical calculations and CALculation of PHAse Diagram (CALPHAD) method by using ThermoCalc software. Directed energy deposition (DED) based additive manufacturing process was used to produce the alloy. After the process parameter determination studies using single-track productions, cuboids were produced. The microstructural investigations showed that while the central region of cuboids has large grains, the outer region has a dendritic structure with some unmolten Mo powders. Although columnar grain formation, which is the general characteristic of directional solidification, was observed at some points, irregularly shaped grains were dominant in the structure. Moreover, there were micron to nano-sized Hf-Ti-O particles inside the grains and especially around the grain boundaries. X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses confirmed the formation of disordered body-centered cubic (BCC) Hf5Mo15Nb35Ta25Ti20 alloy with ∼6 vol% of Hf-Ti-O particles. Electron backscatter diffraction (EBSD) analyses indicated that there is a slight texture in the building direction along 〈111〉. In order to determine the stability of these alloys, ex-situ heat treatments coupled with XRD studies were conducted. As opposed to CALPHAD calculations it was not observed any HCP phase formation. Compression test results showed that Hf5Mo15Nb35Ta25Ti20 alloys have high strength (σy = ∼1300 MPa) and high compressive ductility with good strain-hardening ability. Theoretical calculations revealed that the strength of the alloy mainly originated from solid solution strengthening.

Development of a low-density Co-Ni-Al-Ta-Cr superalloy with high mechanical performance and superior oxidation resistance

In this study, a Co-30Ni-10Al-6Ta-10Cr alloy was designed based on CALPHAD (Calculation of Phase Diagrams) method targeting high γ′ phase fraction and solvus, and optimal thermal processing window. Experimental results concurred with the calculations and validated Cr as a γ phase-forming element in Co-Ni-Al-Ta-based alloys. The incorporation of Cr in the alloy helps mitigate lattice misfit, coarsening rate, and alloy density, while enhancing microstructural stability. A certain amount of Cr led to the development of a superalloy with both high mechanical performance γ′ solvus and low density. Moreover, the oxidation resistance of the Co-Ni-Al-Ta-based high-temperature alloy can be substantially elevated by the introduction of Cr. At 1000 °C, the Co-30Ni-10Al-6Ta-10Cr alloy displayed comparatively low oxidation weight gain, which signifies its excellent oxidation resistance. This is mainly attributed to the formation of continuous (Co,Ni)(Al,Cr)2O4 spinel oxide layers during prolonged oxidation.