Journal of Phase Equilibria and Diffusion最新文献

Thermodynamic databases are indispensable in providing phase equilibria and phase transformation for new alloys design and process optimization. The quality of calculated results is strongly dependent on the accuracy of the thermodynamic database. A thermodynamic database for multicomponent copper alloys has been developed, which contains 30 elements covering the major and minor alloying elements of most commercial copper alloys. About 330 binary and 60 ternary systems have been assessed over the entire composition range. Examples of assessments and calculations for typical binary and ternary systems were presented. A wide range of compositions from pure copper to complex commercial copper alloys can be calculated. Scheil solidification simulations were carried out using the thermodynamic database for predicting the phase formation sequence during solidification, as well as phase compositions and phase fractions. In conjunction with a compatible kinetic database, the present established thermodynamic database was used to simulate the microstructure evolution of copper alloys during the ageing process. The simulated results were verified by key experiments, which proves the accuracy of the thermodynamic database established by us.

A thermodynamic description of the intermetallic phases in the Fe-Cr-Mo-Ni system is presented based on previously unpublished experimental data in the Cr-Mo-Ni system. A review of experimental information from literature together with the new data provides a reliable base for the assessment. Together with previously published alloy systems, an open database for the Fe-Cr-Mo-Ni-N system is provided. Reliable calculations of the stability of the σ phase in the quaternary Fe-Cr-Mo-Ni system are shown, in support for predicted phase equilibria in super-duplex stainless steel.

The CALPHAD method provides an effective way to parameterize alloy free energies computed from first-principles. While the Special Quasirandom Structure (SQS) formalism offers a natural and efficient tool to generate input data for disordered solid solution phases, accounting for Short Range Order (SRO) effects in a computationally efficient way presents a challenge. In this work we introduce a Python based software pipeline which utilize the Cluster Variation Method (CVM) method in tandem with the SQS formalism to determine closed-form nonlinear expressions for temperature-dependent SRO corrections to the formation free energies. Our approach, which implements the CVM to any level of accuracy, has been integrated into the sqs2tdb software pipeline. As a proof of concept, we perform a thermodynamic assessment of the Ir-Ru binary alloy with SRO correction and show its effectiveness in accurately reproducing the known experimental phase diagram. We also perform SRO corrections to an equimolar MoNbTaVW SQS and show significant SRO effects at temperatures far above room temperature.

The phase diagram of the CaO-SiO₂-Nb₂O₅-Fe₂O₃-TiO₂ slag system has important significance for guiding the recycling and utilization processes of metallurgical slags containing niobium and titanium. In this paper, high-temperature equilibrium experiments were conducted at 1100 °C in air atmosphere to investigate the phase equilibria of the CaO-SiO₂-Nb₂O₅-Fe₂O₃-TiO₂ slag system. According to the experimental results, the liquidus surfaces of the liquid + CaTiO₃ and liquid + SiO₂ equilibrium coexistence regions in the CaO-SiO₂-Nb₂O₅-5wt.% Fe₂O₃-TiO₂ system at 1100 °C in air atmosphere were determined using interpolation and function fitting methods. Finally, the 1100 °C isothermal phase diagrams of the CaO-SiO₂-Nb₂O₅-5 wt.% Fe₂O₃-TiO₂ system were plotted. The composition range of liquid phase region was determined, and the positional relationships of the seven other equilibrium coexistence regions were illustrated.

A phase field model is developed to study the discontinuous (cellular) precipitation (DP) reaction in a hypothetical A-B miscibility gap system. Unlike previous treatments, the model employs an interaction energy term which couples the composition and the phase field variable to enable the necessary grain boundary movement. The influence of factors such as interaction energy, interfacial mobility and grain boundary diffusivity on the transformation rate and overall microstructure evolution are discussed.

The method of constrained equilibria has already found extensive use for a good number of years in conjunction with the programmers library ChemApp and freely adaptable ASCII based thermodynamic datafiles. In the present paper a method is demonstrated which permits the application of this method in the framework of the Integrated Thermodynamic Databank System (ITDS) FactSage. Both, modules which interact with the databases and modules which carry out thermodynamic calculations are used, thus emphasizing the aspect of integration in the ITDS. In the paper a link will be established between original thoughts by J.W. Gibbs concerning the definition of the components of a system and kinetic inhibitions in the system and the method of constrained equilibria as such. Furthermore, reference is made to Mats Hillerts use of driving forces in complex (non-)equilibrium cases. A number of application cases with different degrees of complexity will be demonstrated. These range from partially or fully constrained complex equilibrium calculations to phase diagrams with new types of axis variables.

Lack of coating adhesion and bare spot defects of hot-dip galvanized steel plates were experimentally investigated, and the Fe-Al alloy layer was analyzed by both experimental methods and kinetic calculations. Scanning electron microscopy, electron probe micro-analyzer and glow discharge spectrometer method were utilized to determine the microstructures and the distribution of elements of the galvanized steel plates. It is discovered that lack of coating adhesion and bare spot defects depend on the quality of the Fe-Al alloy layer. Fe-Al alloy layer (alias inhibition layer) affects the adhesiveness of the alloy coating to the steel plate, and prevents the interdiffusion process of elements between the zinc pot and the coated steel. The kinetic analysis was carried out by means of CALPHAD (CALculation of PHAse Diagrams) method. Because the main constitutuent of Fe-Al alloy layer is Fe₂Al₅ phase when the Al content in the liquid Zn is kept below 1 wt.%, diffusion models with Fe₂Al₅ were constructed to investigate the element distribution during the galvanizing process, and the calculated results can reasonably predict the element distribution trend in both the alloy coating and the steel plate. It is shown that besides the wetting reactions of Fe and Al during the galvanizing process, the diffusion behavior of elements also influences the coating quality. In summary, the appropriate control of Fe-Al alloy layer can prominently benefit the surface quality of the galvanized coatings, and the manufacturing parameters, such as strip speed, galvanizing time and zinc pot temperature, act as important factors on the formation of the Fe-Al alloy layer. The optimum combination of the aforementioned parameters may contribute to the improvement of the coating quality.

Graphical Abstract

The liquidus surface, melting diagram (superposition of the liquidus and solidus surfaces) and Scheil diagram of the Hf-Rh-Ir system are presented for the first time based on results of the study of as-cast alloys using optical microscopy, scanning electron microscopy, electron probe microanalysis, differential thermal analysis and x-ray diffraction techniques taking into account the constitution of the solidus surface. In the Hf-Rh-Ir system a continuous series of solid solutions between isostructural compounds Hf₂Rh and Hf₂Ir (with the Ti₂Ni-type structure), high-temperature modifications of compounds HfRh and HfIr (CsCl-type), HfRh₃ and HfIr₃ (AuCu₃-type), iridium and rhodium (Cu-type), as well as solid solutions based on βHf, compounds Hf₅Ir₃ and Hf₃Rh₅ take part in phase equilibria. Two invariant four-phase reactions (peritectic at 1958 °C and transition at 1655 °C) involving liquid and corresponding three-phase equilibria take place in this system.