Journal of Phase Equilibria and Diffusion最新文献

The isothermal sections of the Al-Cr-Mo ternary system at 1200 and 1000 °C were experimentally determined based on microstructure and phase constituents from the equilibrated alloys employing electron probe microanalysis, scanning electron microscopy, and x-ray diffraction. A new ternary compound phase named η with AlTi₃-type crystal structure covering a composition range with ~ 75 at.% Al was detected in these two investigated isothermal sections in the present work. Based on the experimental results and the published data of the three binary sub-systems, a thermodynamic description for the Al-Cr-Mo system was carried out using the CALPHAD (CALculation of PHAse Diagrams) method. The newly detected ternary phase η was modeled by a two-sublattice model of (Al)₃(Al,Cr,Mo)₁. A set of reliable thermodynamic parameters of the Al-Cr-Mo system was obtained, which are in satisfactory agreement with the experimental data. Based on the obtained thermodynamic parameters, much information related to the stable vertical sections, isothermal sections, liquidus projection, and miscibility gap of the bcc phase were predicted in the present work. The present work can provide essential experimental and thermodynamic data for the establishment of the Ni-Al-Cr-Mo based alloy database.

This work aims to computationally explore the diffuse prerequisites for σ phase precipitation in high-alloyed duplex steels. The diffusion control for the early precipitation stage of the σ phase was studied by the Calphad thermodynamic modeling combined with the DICTRA software. Different nucleation sites, α/γ, and α/α and γ/γ grain-boundaries, were studied using thermodynamic and mobility databases developed by the present authors in previous works for high-alloyed duplex stainless steel. Simulation results were compared to experimentally obtained microstructures of aged samples. The study of the concentration profiles of the elements Cr, Mo, and Ni revealed that the precipitation is most favorable within the α phase due to fast mobility and strong thermodynamic driving force favoring the formation of the σ phase. Based on the present results, the role of the different heterogeneous sites for the precipitation of the σ phase in hyper duplex steel is discussed.

Phase equilibria in the Mn-Zn binary system were experimentally determined by chemical composition examination, crystal structure determination, and thermal analysis. Major changes were detected for the β, ε, and δ phases. The β-B2 single-phase region could not be confirmed in the studied system because a disordered body-centered cubic structure, which is identical to the δMn phase, was confirmed in a quenched sample from the previously proposed region of β phase. The ε phase has been controversial whether the phase is separated into ε, ε₁, and ε₂ phases or not. By studying a diffusion couple and several alloy compositions, it was established that the ε, ε₁, and ε₂ phases are not separate and comprise a single ε phase. Furthermore, the δ phase is not present in the Zn-rich region of the system because the corresponding invariant reactions were not detected via thermal analysis.

Recent design and development of precipitate reinforced refractory metal alloys demonstrate the possibility of A2 + B2 bcc superalloys as a new class of high temperature materials. Existing β-Ti alloys do not typically employ reinforcement with intermetallics, as in other high temperature alloys; to this effect sufficient additions of Fe, a low cost β-Ti stabiliser, can promote formation of an ordered-bcc intermetallic phase, β′-TiFe (B2), offering scope to develop a β + β′ dual-phase field. However, key uncertainties exist in the base Ti-Fe binary. The current research evaluates the formation of ordered-bcc TiFe precipitates within a disordered-bcc β-Ti matrix through variable heat treatment strategies. The microstructure optimisation has revealed new insight into the Ti-Fe phase equilibria at near eutectoid temperatures in the purported dual-phase field, where a complex interplay between β-Ti, β′-TiFe and α-Ti exists.

There exists strong experimental evidence that bainitic ferrite is formed as a supersaturated solid solution of carbon within a tetragonally-distorted body-centered iron structure (BCT), where carbon preferentially occupies the octahedral site. Despite this, the BCT structure has not yet been accounted for in the computational analysis of the thermodynamics of the bainite transformation. In the present work, we propose to calculate the onset of the bainite transformation based on the T₀′ concept, including the effect of Zener-ordering. This mechanism stabilizes the BCT structure, makes it energetically more favorable than BCC and leads to a significantly higher solubility of C compared Fe-BCC. The computational predictions are made based on a recent reassessment of low-T Gibbs energies and finally compared to experiments. The important role of C is emphasized, with the Fe-C system used as a showcase.

The quasi-ternary system Cu₂Se-In₂Se₃-CuI has been investigated by x-ray diffraction and differential thermal analysis. The isothermal section at 770 K and the liquidus surface projection of the system have been built. For the first time, the primary crystallization regions, and the coordinates of the invariant and monovariant equilibria have been determined. In the system, the regions of the solid solutions based on the binary, ternary, and quaternary compounds have been investigated. The formation of the CuIn₂Se₃I quaternary compound, which melts congruently at 1213 K and has a homogeneity region of 15 and 9 mol.% CuI within the composition triangle has been established. For the first time, the crystal structures of CuGa₂Te₃I and AgGa₂Te₃Br compounds have been studied using a powder method. They crystallize in the tetragonal symmetry, Space Group I-4, a = 5.9147(4) Å, c = 11.952(2) Å for CuGa₂Te₃I; a = 6.2977(3) Å, c = 11.9473(7) Å for AgGa₂Te₃Br compound, respectively. The connection of their structures with the structures of the defective diamond-like semiconductors has been discussed.

The paper proposes a method based on a combination of the provisions of the phonon theory of liquid, V–T formalism, and Frenkel’s theory of determining the P–T parameters of a liquid system, to determine the pressure and temperature values at which the transition from a denser liquid fraction to a less dense one occurs. Its use makes it possible to analyze the motion of fluid components in joint complexes and to determine their lifetime. It is also shown that at short time intervals, regardless of the physical state of the system, the components of the liquid move as independent particles, and their motion can be represented within the framework of the vibrational-hopping diffusion model. In this paper, the developed methodology is used to study the structural and dynamic properties of argon near the triple point on the liquid–gas coexistence curve.

The doping with Cu in the Sb-Se material system can effectively reduce power consumption and improve data retention ability of the PCRAM (Phase-Change Random-Access Memory) material. However, no thermodynamic study of the Cu-Sb-Se system has been reported. Therefore, in this work the Cu-Sb-Se system was modeled using the CALPHAD (CALculation of PHAse Diagrams) method. The excess Gibbs energies of solution phases, including liquid and FCC were expressed by the Redlich-Kister polynomial. Two-sublattice model (Cu,Se)₂Se was used to describe the solid solution of binary intermetallic compounds, i.e. α-Cu₂Se and β-Cu₂Se in Cu-Sb-Se ternary system. The compounds, e.g. η(Cu₂Sb), β(Cu₃Sb), Sb₂Se₃, α-CuSe, β-CuSe, Pe(Cu₃SbSe₄) and C(CuSb₃Se₅) were described as stoichiometric compounds. The temperature of the eutectic reaction γ(Cu₁₇Sb₃) = (Cu) + δ(Cu₄Sb) in the Cu-Sb system and the temperature of the invariant reaction L1 = L2 + (Sb) in the Sb-Se system were adjusted. A set of self-consistent thermodynamic parameters for the Cu-Sb-Se system was obtained, and the 623, 673, 723, 773, 873 and 973 K isothermal sections, and the liquidus projection and invariant reactions for this ternary system have been calculated.