Journal of Phase Equilibria and Diffusion最新文献

The rare earth–iron–transition metal systems are of increasing interest in the search for novel permanent magnet phases. This work reports on the solidification behavior, phase equilibria and stability range of solid phases in the ternary Ce-Fe-Ti system, focusing on the iron-rich region (> 65 at.% Fe) of the isothermal section at 1000 °C. Two ternary phases Ce_1.03Fe_12-xTi_x (x = 0.87–1.02) with ThMn₁₂ structure type and Ce_3.06Fe_27.6Ti_1.4 with Nd₃Fe₂₉ structure type were observed. Magnetic measurements of Ce_1.03Fe_12-xTi_x and Ce_3.06Fe_27.6Ti_1.4 revealed ferromagnetic ordering with Curie temperatures of 550 K and 327 K, respectively.

The equilibrium compositions of all phases in the Ni-rich region of binary Ni-Ce and ternary Ni-Ce-X (X = Al, Nb, Cr, Ti) systems at 900 °C were determined experimentally through isothermal annealing for up to 500 h and compared with currently available computational thermodynamic descriptions. Additionally, the study examined how adding a third element to the binary system affects the microstructure by analyzing changes in the volume fraction of the intermetallic phase in the eutectic region. It was observed that Nb and Ti addition lowered the intermetallic fraction in the eutectic region while Al and Cr addition did the opposite. The fraction of intermetallic phase in the eutectic region is very important because it contributes to extreme brittleness of these alloys. Also, Al, Nb and Ti addition promoted different precipitates upon annealing when added in sufficient amounts. The collected data on composition and phase equilibria provides crucial information for improving the thermodynamic assessments of the binary and ternary alloy systems.

Maraging steels are known to achieve the best mechanical properties when aged around 480 °C. However, the precipitate formation process is still not straightforward enough at this temperature. In this research, Mössbauer spectroscopy, complemented with transmission electron microscopy, x-ray diffraction, hardness measurements, and optical microscopy techniques, was used to investigate the phase transformation process of solution-treated and 480 °C-aged Maraging-300 steel specimens. The results indicated that the precipitation of intermetallic compounds starts at the early stages of aging and that these precipitates are Fe-free, which are responsible for improving mechanical properties. Atomic mobility is discussed, and precipitate formation is evidenced. Small amounts of reverted austenite due to precipitate dissolution were detected at longer aging times, and the formation of paramagnetic iron-rich phases is also suggested.

The utilization of integrated computational materials engineering (ICME) using third generation calculation of phase diagrams (Calphad) databases holds promise for predicting thermodynamics of materials, leading to time and cost-efficient approaches. This study delves into the complexities of stacking fault energy (SFE) in Fe-Mn binary system using the concept of a 3rd generation Calphad database which is suitable for thermodynamic calculations at low temperatures. Releases of 3rd generation Calphad descriptions for unary Fe and Mn in recent years, motivated the authors to address the SFE using a re-assessment of thermodynamic description for the Fe-Mn binary system. The obtained SFE values are calculated thermodynamically and discussed in relation to the material's behavior and properties. SFE values are computed through a revised thermodynamic method of Olson-Cohen, and the relationship between this quantity and properties of material is discussed. This research not only serves to augment our understanding of SFE and related physical phenomena but also identifies regions where thermodynamic databases can be refined. The effectiveness of ICME and Calphad methodologies is demonstrated, contributing to the advancement of materials design and, consequently, the enhancement of performance and reliability in low-temperature applications.

The phase equilibria of the La-Co-Ti ternary system were investigated through the equilibrated alloy method using scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD). The phase formation in La-Co-Ti alloys annealed at 873 K and 1073 K was determined by using the EDS composition measurements and the XRD Rietveld refinements. Five La-Co binary intermetallic compounds (LaCo₁₃, LaCo₅, β-La₂Co₇, La₂Co₃, La₂Co_1.7) and five Co-Ti binary intermetallic compounds (Co₃Ti, Co₂Ti(h), Co₂Ti(c), CoTi and CoTi₂) were observed, while the intermetallic compound La₅Co₁₉ was not found. Two ternary intermetallic compounds La₂Co_17-xTi_x (0.5 ≤ x ≤ 1.3) with a Th₂Zn₁₇-type structure and LaCo_12-xTi_x (1.5 ≤ x ≤ 1.7) with a ThMn₁₂-type structure were detected at 873 K, while the ternary intermetallic compound La₂Co_17-xTi_x (0.5 ≤ x ≤ 1.3) is only existent at 1073 K. Furthermore, the measured phase compositions show that the solubility of the third element in the La-Co and Co-Ti binary intermetallic compounds is negligible (less than 1 at.%). Two isothermal sections of the La-Co-Ti ternary system at 873 K and 1073 K were constructed finally.

This article considers recent progress in modelling the degradation of Fe9Cr steels exposed to high-temperature CO₂. Computational modelling is used to rationalise the mechanism of the so-called breakaway oxidation, which is shown here to be associated with the carburisation of the underlying Fe9Cr substrate of finite dimensions. Oxidation kinetics, non-steady-state carburisation kinetics, and the mass transport mechanisms are covered. The theoretical and numerical/analytical challenges are discussed, with possible ways forward being suggested. Thus, we demonstrate that the software systems built on Prof. Hillert’s legacy are maturing rapidly towards engineering tools which can be used to anticipate the degradation of complex multicomponent alloys in engineering situations of relevance and significant complexity.