Journal of Phase Equilibria and Diffusion最新文献

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.

The quantification of the role of alloying elements on interface migration during phase transformations in steels and selected non-ferrous alloys (e.g., Ti-based) remains an active area of research that was inspired by seminal contributions of Mats Hillert. In previous studies we had introduced atomistically informed solute drag models for simulation of grain growth and recrystallization. In the present study this approach is extended to diffusional phase transformations where a fast-diffusing species (e.g., C in Fe) redistributes between the parent and daughter phases. The proposed methodology is demonstrated with a conceptional analysis of nano- and mesoscale phase field simulations for model binary and ternary alloys. The approach is shown to be consistent with the formulations of the Hillert–Sundman solute drag model. The challenges in applying this simulation approach to experimental data are critically discussed.

Preparation conditions play a key role in tailoring the properties of ceramic materials, including ferrite, to suit efficient industrial and technological applications. This manuscript is concerned with correlating the structural, spectroscopic, optical, transport, and dielectric properties of nickel zinc ferrite nanoparticles (NZNs) to the sintering temperature as an effective preparation condition controlled through the coprecipitation technique. Techniques for studying the various features of the synthesized compounds include x-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, Fourier-transform infrared spectroscopy, ultraviolet-visible spectroscopy, and the LCR bridge. XRD data showed the as-prepared samples' single-phase inverse spinel structure and an increase in crystallinity with increasing sintering temperature. SEM images show the nanosized range with semi-spherical particles for all the NZN fabricated samples. Moreover, Raman spectroscopy results showed that the four distinct active modes (Eg, F2g(2), A1g(2), and A1g(1)) for the NZN compounds have the same lattice strain tendency. The direct and indirect optical energy gap values (2-3.82) eV of the synthesized compounds span a wide range in the visible and ultraviolet spectrum, making them candidates for optoelectronic applications. In general, sintering temperature plays an outstanding role in increasing the values of some features such as crystallite size, optical energy gap, and electrical conductivity, and correspondingly decreasing other features such as unit cell volume dissociation density, absorption bands, and dielectric parameters.

Diffusion is one of the key research interests in developing advanced materials and processes, but acquisition of diffusion coefficients is a bottleneck. Hereby we propose a hybrid scheme that couples the molecular dynamics (MD) simulation for calculating tracer diffusion coefficients, with the CALPHAD method providing experimental benchmarks for pure metals and assessing atomic mobilities. After verifying the scheme by studying the fcc Ni-Co-Fe ternary alloys (including its pure components and binary sub-systems) at 1600 K, for which sufficient amount of experimental data as well as the CALPHAD assessments are available, this scheme demonstrates the ability of establishing a mobility database efficiently with reduced experimental efforts. In order to reconcile the MD simulations with the experiments, a priority is to determine impurity and self-diffusion coefficients for pure metals by CALPHAD assessments of the experimental data from the literature as benchmarks and thus set up a set of elemental bases for pure metals. Then all the MD calculated tracer diffusion coefficients were normalized accordingly, followed by the CALPHAD assessments to develop an atomic mobility database, from which all types of diffusion coefficients can be readily calculated.

The Ga₂O₃-SnO₂-ZnO (GSZO) system has been studied by Knudsen effusion mass spectrometry (KEMS) in the temperature range 1305-1495 K. The incongruent character of vaporization processes in the whole composition range of the GSZO system was observed. The main thermodynamic characteristics of heterogeneous equilibria in the system have been determined, as well as the standard enthalpies of reactions involving Zn₂SnO₄ and ZnGa₂O₄ spinels. A p–x vertical section of the phase diagram of the GSZO system has been plotted along the GaO_1.5 and SnO₂ equimolar ratio line.

Kinetics of the (gamma) /(gamma ^{prime}) phase transformation and the interdiffusion phenomena in single-crystal Ni-based superalloys, under isothermal annealing and composition gradient, is investigated through the phase-field and continuum diffusion models. The employed models in the present work exploit CALPHAD-based thermodynamics and kinetics databases, in order to perform realistic simulations. We specifically predict the interdiffusion of elements for a hypothetical alloy AlCoCrTaNi/Ni diffusion couple, equivalent to the CMSX-10/Ni diffusion couple, at 1323 K. Accordingly, the phase fraction and morphology of (gamma ^{prime}) precipitations in the (gamma) matrix is simulated as well. The implemented multi-component diffusion model takes into account vacancies and pore formation, reflecting Kirkendall effect. Furthermore, the time evolution of morphology parameters of the precipitate-depleted zone in the diffusive region (i.e., the position and the size) are estimated.