Journal of Phase Equilibria and Diffusion最新文献

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 energy crisis and climate change have promoted a growing interest in non-fossil sources, such as nuclear, with uranium carbides being seen as potential fuel candidates for Generation IV nuclear reactors. However, the need of accurate thermophysical data for the fuel and its compatibility with core materials during the extreme fission conditions is still an issue. Here a study of the ternary uranium-iron-carbon system performed at 1100 °C using powder x-ray diffraction and Scanning Electron Microscopy coupled with Energy Dispersive Spectrometry is presented. The U-Fe-C isothermal section is characterized by two ternary compounds, thirteen 3-phase regions and five 2-phase regions. UFeC₂ and ~ U₁₁Fe₁₂C₁₈ were confirmed to be present at 1100 °C and crystallize in structures related to the binary uranium carbides. UFeC₂ crystallizes in an original structure type, a distorted variant of the UCoC₂ structure, with space group P4/n and a = 3.503(5) Å and c = 7.405(5) Å lattice parameters. ~ U₁₁Fe₁₂C_18, has a crystal structure related to the Th₁₁Ru₁₂C₁₈ structure-type (space group I (overline{4 }) 3m) with the lattice parameter a ≈ 10 Å. Furthermore, an island of a α-UC₂-based phase with 32U:4Fe:64C composition was found in the 1100 °C isothermal section, indicating the inclusion of Fe in the α-UC₂ binary compound.

Ternary alloys samples with 22, 25 and 23 different compositions were prepared for determining isothermal sections at 1123, 1223 and 1373 K, respectively. The microstructures, phase constituents and phase compositions of the annealed Cu-Nb-Ni alloys were analyzed by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD) methods. Two three-phase regions, (text{fcc} + {text{NbNi}_{{3}}}+{text{Nb}_7}{text{Ni}_6}), fcc + bcc(Nb) + Nb₇Ni₆, and three two-phase regions, (text{fcc} + {text{NbNi}_{{3}}},{text{Nb}_7}{text{Ni}_{{6}}}+{text{NbNi}_{{3}}}), fcc + Nb₇Ni₆, are determined for isothermal sections at 1123 and 1223 K. Two three-phase regions, (text{liquid} + {text{NbNi}_{{3}}}+{text{Nb}_7}{text{Ni}_6}), liquid + bcc(Nb) + Nb₇Ni₆, and three two-phase regions, (text{fcc} + {text{NbNi}_{{3}}},{text{Nb}_7}{text{Ni}_{{6}}}+{text{NbNi}_{{3}}}), liquid + Nb₇Ni₆, are determined for isothermal sections at 1373 K. The solubilities of Cu in NbNi₃ and Nb₇Ni₆ were determined to be ~ 9.6 at.% and ~ 11.4 at.% at 1123 K, ~ 10.8 at.% and ~ 12.4 at.% at 1223 K and ~ 11.2 at.% and ~ 12.8 at.% at 1373 K, respectively. No ternary compounds were found. Based on the experimental phase equilibria data from the literature and the present work, a thermodynamic description of the Cu-Nb-Ni system was carried out by CALPHAD method. The substitutional solution model and sublattice model were employed to describe the solution phases and intermediate phases, respectively. A set of self-consistent thermodynamic parameters of the Cu-Nb-Ni system was conclusively obtained. Most of the reliable experimental data were reproduced by the present thermodynamic modeling.

Combination of the experimental measurements of diffusion behavior and kinetic computational simulation provides a unique tool to probe the design of multi-component refractory alloys with excellent properties. In this work, for the first time, the determination of the interdiffusion coefficients of bcc phase in Mo-Zr system and Mo-Nb-Zr ternary system as well as the relevant atomic mobility parameters of Mo, Nb and Zr in BCC phase are investigated systematically. The interdiffusion coefficients of bcc phase in Mo-Zr binary alloys and Mo-Nb-Zr ternary alloys at 1423-1523 K were measured by solid-phase diffusion couple method combined with Boltzmann-Matano method and Matano-Kirkaldy method, respectively. Simultaneously, the quite steep Mo concentration gradients of the corresponding ternary diffusion couples in the Mo-Nb-Zr system are observed in this study, and the contributions of which are carefully evaluated in the subsequent extraction of the ternary interdiffusion coefficients for the Mo-Nb-Zr system. On the basis of the determined interdiffusion coefficients of Mo-Zr system and Mo-Nb-Zr system in this work, along with the relevant thermodynamic parameters, the atomic mobility parameters of Mo, Nb and Zr in BCC phase were evaluated, which are incorporated into the atomic mobility database of bcc phase in Nb-Mo-Ti-Zr multi-component system. In addition, the component distance curves of a series of diffusion couples are simulated by applying the established atomic mobility database. The consistency between the simulated results and the measured values further verifies the reliability of the work.