Journal of Phase Equilibria and Diffusion最新文献

In this work, the phase equilibria of the binary Ag-In system were determined using electron probe microanalysis and differential scanning calorimetry on equilibrated alloys and diffusion couples. The compositions of the phase boundaries of solid phases that are highly scattered in the literature have been precisely determined. The temperatures of the invariant reaction ζ ⇄ γ + L and the polymorphic transformation ζ ⇄ γ are substantially lower than previously reported values. In addition, it was found that the In-rich ζ phase phase-separates after months of room-temperature aging.

In non-ideal solutions, partial molar volumes change with composition, which means a diffusion process is always accompanied by change in volume of the system. To account for this change in volume while solving diffusion equation, it is necessary to know the velocity of the local center of volume (({U}^{V})). An expression is derived for ({U}^{V}), using a treatment that is applicable to a multicomponent system. Simulations of multicomponent diffusion profiles with composition dependent partial molar volumes have been absent in the literature so far. The expression derived in this work is also used to generate diffusion profiles in a hypothetical ternary diffusion couple. Significant difference is observed between the concentration profiles obtained with and without the assumption of constant molar volume. Exact calculation of ({U}^{V}) also enables the estimation of the expansion or contraction accompanied by diffusion, which in turn would help in assessing diffusion induced stresses and dimensional changes.

Multicomponent phase space has been shown to consist of an enormous number of materials with different compositions, the vast majority of which have never been made or investigated, with great potential, therefore, for the discovery of exciting new materials with valuable properties. At the same time, however, the enormous size of multicomponent phase space makes it far from straightforward to identify suitable strategies for exploring the plethora of potential material compositions and difficult, therefore, to be successful in discovering desirable new materials. Unfortunately, all our knowhow and understanding has been developed for materials with relatively few components in relatively limited proportions, with most of our scientific theories relying essentially on linear assumptions of component dilution and independence that no longer apply in concentrated multicomponent materials. Trial and error, controlled substitution, parameterisation, thermodynamic modelling, atomistic modelling and machine learning techniques have all been employed as methods of exploring multicomponent phase space, with varying levels of success, but ultimately none of these techniques has proved capable of delivering consistent or guaranteed results. This paper provides an overview of the different techniques that have been used to explore multicomponent phase space, indicates their main advantages and disadvantages, and describes some of their successes and failures.

The phase equilibria of the Er-Al-Zr ternary system at 500 °C were investigated using a combination of electron probe microanalyzer and x-ray diffraction. The microstructure and diffraction peaks were analyzed to determine the phases and compositions of Er-Al-Zr ternary system. Based on the experimental results, the isothermal phase diagram of the Er-Al-Zr ternary system consists of 14 three-phase equilibrium regions, 15 two-phase equilibrium regions, and 13 stable binary compounds, but no ternary compounds were detected. The solubility of Er in the Al₂Zr, Al₃Zr₂, AlZr, Al₃Zr_4, Al₂Zr₃ is 9.9, 5.3, 9.0, 12.4, 6.7 at.%, respectively. The present work could be important for alloy design of Al-based alloys and thermodynamic analysis of the Er-Al-Zr ternary system.

Phases and equilibria involved in the isothermal section at 500 °C of the ternary Al-Fe-Pr system have been here investigated in the whole composition range by means of X-ray diffraction, optical and scanning electron microscopy, and electron probe microanalysis. Phase equilibria are characterised by the formation of two binary solid solutions, Pr₂(Fe_xAl_1−x)₁₇ with 0.34 ≤ x ≤ 1.00 (hR57–Th₂Zn₁₇) and Pr(Fe_xAl_1−x)₂ with 0 ≤ x ≤ 0.20 (cF24–Cu₂Mg), and four ternary compounds, τ₁-PrFe₂Al₁₀ (oS52-YbFe₂Al₁₀), τ₂-PrFe₂Al₈ (oP44-CeFe₂Al₈), τ₃-Pr(Fe_xAl_1−x)₁₂ with 0.28 ≤ x ≤ 0.44 (tI26-ThMn₁₂) and τ₄-Pr₆(Fe_xAl_1−x)₁₄ with 0.63 ≤ x ≤ 0.81 (tI80-La₆Co₁₁Ga₃), which have been confirmed. The solid solubility ranges of the binary and ternary compounds have been considered and trends of their lattice parameters studied. The complete isothermal section has been obtained and the general features of the section are discussed and compared with those of other ternary systems of light R (La, Ce, Pr, Nd, Sm) with Al and Fe.

A thermodynamic description of the Ti-Al-Fe system was established with reassessed Ti-Al and Ti-Fe binary systems using density function theory (DFT) data. All stable and metastable end members of BCC_B2, BCC_D0₃/B32, BCC_L2₁, inverse BCC_L2₁, Laves C14, D0₁₉-Ti₃Al, L1₀-TiAl, Ti Al₂, Ti₃Al₅, D0₂₂-TiAl₃, τ₂ and τ₃ in the Ti-Al, Ti-Fe and Ti-Al-Fe systems were energetically defined with available experimental data and DFT calculations, reaching reasonable consistency. The ternary description was used to successfully calculate the A2-B2-L2₁ transformation in Fe-rich corner and A2-B2 transformation in Ti-rich corner, allowing the design of Ti-rich and Fe-rich alloys in this system.

The microstructures and properties of foundry alloys designated by the generic term “cast irons” are highly diverse, even if we limit ourselves to so-called silicon cast irons, which are essentially quasi-eutectic Fe-C-Si alloys. This diversity is compounded by the fact that these microstructures appear partly during solidification and partly during solid-state transformations. Throughout the scientific career of Mats Hillert, his attention has been drawn to the wide range of phenomena involved in the formation of cast iron microstructures during solidification, as the present review of his contributions in this field shows. In addition, much of his work on the solid-state transformations of steels has found—or should find—an echo in the description of the matrix microstructure of graphitic cast irons, which is the subject of the final part of this article.

Reliable thermodynamic and kinetic databases are essential for designing and developing novel magnesium (Mg) alloys for elevated-temperature applications in the automotive and aerospace industries. This study investigated diffusion behaviors of HCP Mg-Ag-Sn alloys by four sets of three diffusion couples annealed at 450, 500, and 550 °C, respectively. Interdiffusion and impurity diffusion coefficients at the three annealing temperatures were extracted using the forward-simulation method. The determined diffusion coefficients, combined with prior results in the literature, were then used to assess atomic mobilities for the HCP phase of the Mg-Ag-Sn system. This assessment was conducted using the DICTRA and the TCMG5 thermodynamic database within the Thermo-Calc software. Comprehensive comparisons between calculated and experimental diffusion coefficients yielded an excellent agreement. The atomic mobilities were also further validated by appropriate predictions of concentration profiles and diffusion paths observed in independent diffusion couple experiments performed at 525 °C for 18 hrs. It has been found that the addition of Sn and Ag both increase the diffusivity of Ag in HCP Mg and Sn in HCP Mg in the stable temperature range of HCP Mg, respectively. This improved understanding of the kinetics in the Mg-Ag-Sn ternary system is essential for controlling diffusion-dependent properties such as coarsening and, therefore, the mechanical properties of Mg-Ag-Sn alloys at elevated temperatures.

Exploring the correlation between the density and the thermo-physical properties of the Al₂O₃-CaO-MgO-SiO₂ quaternary slag system is a subject of great interest in the domain of high alumina slag systems. This work attempts to establish correlations between (a) molar volume/density with enthalpy of mixing and (b) molar volume/density with slag viscosity, for the quaternary slag systems. The former is targeted based on existing models to determine the slag density and enthalpy of mixing first and then to develop machine-learning models which can suitably extrapolate the enthalpy of mixing as a function of slag composition, temperature and density. The volume shrinkage and the exothermic enthalpy of mixing between the slag constituent components are correlated in the current work. The later part would involve the conjunction of two hybrid machine-learning models, one for predicting slag viscosity as a function of slag compositions and temperature, and the other which predicts slag viscosity with the incorporation of slag density. The work will facilitate the establishment of two novel quantitative relationships that could provide better insights into the blast furnace quaternary slag systems.