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A tailor-made thermodynamic database of the Fe-Mn-Al-C system was developed using the CALPHAD approach. The database enables predicting phase equilibria and thereby assessing the resulting microstructures of Fe-Mn-Al-C alloys. Available information on the martensite start (Ms) temperature was reviewed. By employing the Ms property model in the Thermo-Calc software together with the new thermodynamic database and experimental Ms temperatures, a set of model parameters for the Fe-Mn-Al-C system in the Ms model was optimised. Employing the newly evaluated parameters, the calculated Ms temperatures of the alloys in the Fe-Mn-Al-C system were compared with the available measured Ms temperatures. Predictions of Ms temperatures were performed for the alloys, Fe-10, 15 and 20 wt.% Mn-xAl-yC. The predictability of the Ms model can be further validated when new experimental Ms temperatures of the Fe-Mn-Al-C system are available. [ABSTRACT FROM AUTHOR]

The ternary Co-Al-C system was thermodynamically assessed using the CALPHAD method based on the critical review of all experimental information in the system. The κ-carbide was described with a three-sublattice model (Al,Co)3(Al,Co)1(C,Va)1. To support the assessment, the enthalpies of formation of all end-members of the κ-carbide were studied by ab initio calculations. The solubility ranges of the carbon in the κ-carbide, the αCo and the AlCo (B2) phases were well reproduced. The equilibria involving the liquid phase were reasonably described using the present set of thermodynamic parameters. [ABSTRACT FROM AUTHOR]

The Al-C-Fe system was assessed in the framework of the CALPHAD approach. Through the critical review of thermochemical properties of liquid Al-Fe alloys, the binary Al-Fe description was revised to agree better with the experimental data. The partitioning model based on the Compound Energy Formalism (CEF) was utilized to describe the disordered and ordered bcc, fcc and κ phases. Moreover, ab initio calculations were performed to determine the enthalpies of formation of the ordered structures based on the bcc and fcc lattices in the binary Al-Fe and for the end-members of the κ phase in the ternary Al-C-Fe system. In order to simplify the database, the present work also employed a two-sublattice model to describe the B2 ordered phase in the Al-Fe system, which can be applied easily to diffusion simulations. Comprehensive comparison between the model-predicted and experimental data confirms that the present evaluation describe the Al-C-Fe system satisfactorily, especially the κ phase. [ABSTRACT FROM AUTHOR]

Thermodynamic optimizations have been performed for the Mn–Si binary and Fe–Mn–Si ternary system by the CALPHAD method. Combining the experimental and ab initio calculated data on the enthalpies of formation of manganese silicides, a better description for those silicides has been obtained. Almost all the latest data on phase equilibria in the Mn–Si system were reproduced satisfactorily. Based on the new assessments of the binary sub-systems and the recent experimental data on phase equilibria including martensitic transformations, a reassessment of the Fe–Mn–Si system has been carried out. The optimized parameters of the Fe–Mn–Si system successfully reproduced phase equilibrium data, as well as the T 0 temperature between the fcc and hcp phases. Apart from the thermodynamic evaluation, the interdiffusion coefficients for the fcc phase of the binary Fe–Si and ternary Fe–Mn–Si system have been determined experimentally over the temperature range from 1273 K to 1473 K employing the diffusion-couple technique. Subsequently, atomic mobility data for the fcc phase of the Fe–Mn–Si system have been assessed and most diffusivity data have been satisfactorily described. [ABSTRACT FROM AUTHOR]

In the present work, the thermodynamic description of the Ti–Al–Zr ternary system was assessed by taking into account the ab initio data on the formation enthalpies of end-members of the intermetallic compounds, combined with the available experimental phase equilibria information in literature. The developed thermodynamic description of Ti–Al–Zr system allows to reasonably represent the experimental phase relations, and particularly to describe the solubility of third element in the binary intermetallic compounds well. Upon the newly developed thermodynamic description, the atomic mobility parameters of the bcc_A2 phase for the Al–Zr binary and Ti–Al–Zr ternary were synergistically assessed to fit the experimental diffusion data in literature. The developed atomic mobility enables to reliably derive all types of reportedly diffusion coefficients in literature. The comprehensive comparison made between the model-predicted and diffusion experiments with emphasis on composition profiles and diffusion paths confirms the reliability of the atomic mobility developed in this work. • A thermodynamic description of the Ti–Al–Zr system was successfully assessed. • The associated phase relations of the Ti–Al–Zr system were well described. • The atomic mobility of bcc phase for the Al–Zr binary and Ti–Al–Zr ternary systems were assessed. [ABSTRACT FROM AUTHOR]

The phase equilibria, thermodynamic properties and diffusion mobilities of the Fe-Co system were carefully assessed through the CALPHAD methods. As an indispensable tool, the first-principles calculations were carried out to study the magnetic moments and the enthalpies of mixing of the bcc_A2, bcc_B2, fcc_A1 and hcp_A3 phases as well as the point defect types of the bcc_B2 phase. In order to verify the heat capacities reported in the literature, new measurements were conducted in a high-temperature calorimetric apparatus using the three-dimensional calorimetric method. Because of the revision of the thermodynamic parameters in the present work, the diffusion mobilities for the fcc_A1 phase were reassessed. The diffusion mobilities for the bcc_A2 phase were established for the first time based on the experimental diffusion coefficients. For the low-temperature bcc_B2 phase, the diffusion couple experiments conducted in the present work show that the diffusion process is sluggish and the interdiffusion coefficients are difficult to determine. Therefore the tracer diffusivities of Co and Fe in the Fe-Co alloys were used to assess the diffusion mobilities for the bcc_B2 phase, while the composition-distance profile of one diffusion couple was served as a validation of its diffusion mobilities. [ABSTRACT FROM AUTHOR]

Thermodynamic reassessment of the ternary Fe–Nb–V system was carried out after a critical review of the available experimental and ab initio data. The primary solidified phases of Fe–Nb–V alloys were investigated using scanning electron microscopy and X-ray diffraction analysis. The C14 Laves phase exhibits a wide primary solidification field in the Fe-rich region, which is in contradiction with the experimental observation in the literature. Ab initio calculations were performed to obtain the enthalpies of formation of three intermetallic compounds (i.e., C14 Laves, μ, and σ), which were used to estimate the thermodynamic parameters. The end-member parameters for the three phases were improved in comparison with the previous description. The presently obtained thermodynamic description of the ternary system can reproduce the wide homogeneity range of the C14 Laves phase and the phase equilibria between the intermetallic compounds and bcc phase. • The primary solidified phases of Fe–Nb–V alloys were experimentally investigated. • The formation enthalpies of C14, μ, and σ were obtained by ab initio calculations. • A self-consistent thermodynamic description of the Fe–Nb–V system was obtained. • The wide homogeneity range of the C14 Laves phase was well described. [ABSTRACT FROM AUTHOR]