Assessment of the Cr-B system and extrapolation to the Ni-Al-Cr-B quaternary system

The Cr-B system is re-assessed treating boron as an interstitial element in the disordered solid solution fcc and bcc phases. The binary assessment is in good agreement with the available experimental phase diagram data and thermochemical data. The Cr-B binary assessment is then used in the assessment of the Ni-Cr-B and Al-Cr-B systems. The ternary assessments are in reasonable agreement with the limited experimental data for the systems. Finally, the ternary assessments are combined with the previous ternary assessment of the Ni-Al-B system to extrapolate to the quaternary Ni-Al-B-Cr system.     

The reassessment of the Al-V system and new assessment of the Al-Si-V system

The theoretical assessment of the Al-Si-V system has been carried out and has been presented here. The experimental results from Huber et al. [1,2] were used as the basis of the assessment. The relevant binary system assessments for Al-V [9], Al-Si [13] and Si-V [14] were used in the initial stage of the study and it was found that complete reassessment of the Al-V system was necessary. The reassessed dataset for the Al-V system is in very good agreement not only with existing experimental phase diagram and thermodynamic data, but is also consistent with the independent work of Lindahl et al. [22].The final assessment of the Al-Si-V system using our own reassessed Al-V system is in excellent agreement with the experimental data.     

Modified embedded-atom interatomic potential for Fe-Ni,Cr-Ni and Fe-Cr-Ni systems

A semi-empirical interatomic potential formalism, the second-nearest-neighbor modified embedded-atom method (2NN MEAM), has been applied to obtaining interatomic potentials for the Fe-Ni, Cr-Ni and Fe-Cr-Ni systems using previously developed MEAM potentials of Fe and Ni and a newly revised potential of Cr. The potential parameters were determined by fitting the experimental data on the enthalpy of formation or mixing, lattice parameter and elastic constant. The present potentials generally reproduced the fundamental physical properties of the Fe-Ni and Cr-Ni alloys. The enthalpy of formation or mixing of the disordered phase at finite temperature and the enthalpy of mixing of the liquid phase are reasonable in agreements with experiment data and CALPHAD calculations. The potentials can be combined with already-developed MEAM potentials to describe Fe-Cr-Ni-based multicomponent alloys. Moreover, the average diffusivities in the unary, some binary and ternary alloys were simulated based on present potential. Good agreement is obtained in comparison with experimental data.     

Thermodynamic description of solution phases of systems Fe-Cr-Si and Fe-Ni-Si with low silicon contents and with application to stainless steels

A thermodynamic optimization has been made for the solution phases of the ternary systems Fe-Cr-Si and Fe-Ni-Si in the iron-rich corner. Ternary substitutional-solution interaction parameters were optimized for the liquid, fcc and bcc phases, and the lower-order data were taken from the earlier assessed sub-systems. The calculated results were validated with experiments of phase equilibria and component activities in liquid. The new data were then added to the existing database of multicomponent steels and calculations were carried out for certain silicon containing stainless steels. As a result, clearly improved agreement was obtained between calculations and experiments concerning the liquidus temperatures and the solid/liquid partitioning of silicon in these steels.     

Phase diagram calculation in Co---Cr system using Ab initio determined lattice instability of sigma phase

The calculations of phase equilibria in the Co---Cr system were performed using the CALPHAD method on the basis of a new two-sublattices model of sigma phase. This model enables us to utilise the results of ab initio calculations of total energy differences between the sigma phase structure and the Standard Element Reference (SER) structures of pure metal at the relaxed lattice parameters (Δ⁰E_i^σ−SER). Total energies were calculated by Full-Potential Linear Augmented Plane Waves (FLAPW) method in the General Gradient Approximation (GGA). The entropy contribution to the Gibbs energy of the pure elements in the sigma phase structure, and the excess Gibbs energy of mixing of the sigma phase were adjusted to the experimental phase equilibrium data.     

A pair-wise interaction model of the sigma phase III — a general approach

The pair-wise interaction model of the sigma phase developed and tested in two orevious papers (1,2) is extended in such a way that the compositions of the five sublattices can vary freely, without the artificial constraints employed earlier (1,2). Two further extensions are described: the first of these allows a variation in the length and nature of the counted bonds and the second permits the treatment of systems with more than two components. These extensions should enable this approach to be applied to a wide variety of closely packed alloy phases. Finally this general approach is reapplied to the sigma phase and the results compared with those of the constrained calculations (1,2).     

The study of the Pb–Se–Te phase diagram: Part 2 – The thermodynamic assessment of the Se–Te and Pb–Se–Te systems

Pb–Se–Te ternary system is of significant importance for thermoelectric applications. In spite of this, no systematic experimental or theoretical study of its phase diagram has been carried out up to now. The CALPHAD type theoretical assessment was done in the scope of this work for the Se–Te and Pb–Se–Te systems based on our own experimental work and the experimental results from literature. It was found out that the reassessment of the existing Se–Te phase diagram assessments is necessary because of some discrepancies between the experimental results and calculations for this system. This new dataset was consequently used for the new assessment of the Pb–Se–Te system and very good agreement was reached with existing experimental data.     

Experimental study and thermodynamic assessment of the Zn-Fe-Ni system

The Zn-rich corner of the Zn-Fe-Ni system was experimentally determined. It was found that the T phase, which was believed previously to be an extension of the binary Γ₁ phase in the Zn-Fe system, is a true ternary compound. The composition range of this phase has been determined in this study. Based on the results of the assessments of the Zn-Fe and Zn-Ni systems carried out by the authors and using information on the Fe-Ni system available in the open literature, a preliminary assessment of the Zn-Fe-Ni system was carried out. A two-sublattice model (Fe,Ni,Zn)Zn₅ was used to describe the ternary T phase. The calculated phase boundaries in the Zn-rich corner are in good agreement with experimental results. However, reproduction of the complex homogeneity range of the ternary T phase has proven challenging.     

A thermodynamic reassessment of the Ca–Pb system

New experimental measurements of the mixing enthalpy of the liquid phase and the enthalpies of formation of the intermetallic compounds along with the data already taken into account in previous thermodynamic assessments have been used in a reassessment of the thermodynamic parameters of the Ca–Pb system. The calculations based on the thermodynamic modelling are in good agreement with the phase diagram data and experimental thermodynamic values.     

Mobilities of Ti and Fe in disordered TiFe-BCC assessed from new experimental data

Pure titanium has an HCP structure and lacks mechanical properties for many industrial purposes. The BCC phase of Ti is required to make alloys with increased strength compared to pure Ti. Iron is the most potent element for stabilising the BCC phase. However, the addition of Fe to Ti causes segregation issues during solidification, which can be avoided by diffusion-driven solid-state alloying. To predict the diffusion kinetics, the interaction mobility parameters of Ti and Fe in the disordered BCC phase of Ti are necessary. In this work, these parameters are optimised based on new experimental data from Ti-Fe diffusion couples produced by the Field Assisted Sintering Technology (FAST). Diffusion couples were held at 1173K and 1273K for one hour. High-resolution Fe concentration profiles are obtained from Electron Probe Micro Analyser (EPMA). Ternary mobility interaction parameters are assessed based on binary endmembers with a DICTRA sub-module, and results are compared to earlier assessments of mobilities of the disordered BCC TiFe system.