The forward and reverse phase transformation from face-centered cubic (fcc) to hexagonal close-packed (hcp) in the equiatomic high-entropy alloy (HEA) CrMnFeCoNi has been investigated with diffraction of high-energy synchrotron radiation. The forward transformation has been induced by high pressure torsion at room and liquid nitrogen temperature by applying different hydrostatic pressures and large shear strains. The volume fraction of hcp phase has been determined by Rietveld analysis after pressure release and heating-up to room temperature as a function of hydrostatic pressure. It increases with pressure and decreasing temperature. Depending on temperature, a certain pressure is necessary to induce the phase transformation. In addition, the onset pressure depends on hydrostaticity; it is lowered by shear stresses. The reverse transformation evolves over a long period of time at ambient conditions due to the destabilization of the hcp phase. The effect of the phase transformation on the microstructure and texture development and corresponding microhardness of the HEA at room temperature is demonstrated. The phase transformation leads to an inhomogeneous microstructure, weakening of the shear texture, and a surprising hardness anomaly. Reasons for the hardness anomaly are discussed in detail.

In this work, new oxide dispersion strengthened (ODS) ferritic steels have been produced by powder metallurgy using an alternative processing route and characterized afterwards by comparing them with a base ODS steel with Y₂O₃ and Ti additions. Different alloying elements like boron (B), which is known as an inhibitor of grain growth obtained by pinning grain boundaries, and complex oxide compounds (Y-Ti-Zr-O) have been introduced to the 14Cr prealloyed powder by using mechanical alloying (MA) and were further consolidated by spark employing plasma sintering (SPS). Techniques such as x-ray diffraction (XRD), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) were used to study the obtained microstructures. Micro-tensile tests and microhardness measurements were carried out at room temperature to analyze the mechanical properties of the differently developed microstructures, which was considered to result in a better strength in the ODS steels containing the complex oxide Y-Ti-Zr-O. In addition, small punch (SP) tests were performed to evaluate the response of the material under high temperatures conditions, under which promising mechanical properties were attained by the materials containing Y-Ti-Zr-O (14Al-X-ODS and 14Al-X-ODS-B) in comparison with the other commercial steel, GETMAT. The differences in mechanical strength can be attributed to the precipitate’s density, nature, size, and to the density of dislocations in each ODS steel.

Ion irradiation is a promising tool to emulate neutron-irradiation effects on reactor pressure vessel (RPV) steels, especially in the situation of limited availability of suitable neutron-irradiated material. This approach requires the consideration of ion-neutron transferability issues, which are addressed in the present study by comparing the effect of ions with neutron-irradiation effects reported for the same materials. The first part of the study covers a comprehensive characterization, based on dedicated electron microscopy techniques, of the selected unirradiated RPV materials, namely a base metal and a weld. The results obtained for the grain size, dislocation density, and precipitates are put in context in terms of hardening contributions and sink strength. The second part is focused on the depth-dependent characterization of the dislocation loops formed in ion-irradiated samples. This work is based on scanning transmission electron microscopy applied to cross-sectional samples prepared by the focused ion beam technique. A band-like arrangement of loops is observed in the depth range close to the peak of injected interstitials. Two levels of displacement damage, 0.1 and 1 dpa (displacements per atom), as well as post-irradiation annealed conditions, are included for both RPV materials. Compared with neutron irradiation, ion irradiation creates a similar average size but a higher number density of loops presumably due to the higher dose rate during ion irradiation.

Ion irradiation combined with nanoindentation is a promising tool for studying irradiation-induced hardening of nuclear materials, including reactor pressure vessel (RPV) steels. For RPV steels, the major sources of hardening are nm-sized irradiation-induced dislocation loops and solute atom clusters, both representing barriers for dislocation glide. The dispersed barrier hardening (DBH) model provides a link between the irradiation-induced nanofeatures and hardening. However, a number of details of the DBH model still require consideration. These include the role of the unirradiated microstructure, the proper treatment of the indentation size effect (ISE), and the appropriate superposition rule of individual hardening contributions. In the present study, two well-characterized RPV steels, each ion-irradiated up to two different levels of displacement damage, were investigated. Dislocation loops and solute atom clusters were characterized by transmission electron microscopy and atom probe tomography, respectively. Nanoindentation with a Berkovich indenter was used to measure indentation hardness as a function of the contact depth. In the present paper, the measured hardening profiles are compared with predictions based on different DBH models. Conclusions about the appropriate superposition rule and the consideration of the ISE (in terms of geometrically necessary dislocations) are drawn.

In this work, the extraction of vanadium (V) ions from an alkaline solution using a commercial quaternary ammonium salt and the production of metal vanadates through precipitation stripping were carried out. The crystallization of copper vanadates from the extracts was performed using a solution containing a copper(II) source in concentrated chloride media as a stripping agent. In an attempt to control growth, a stabilizing polymer (polyvinylpyrrolidone, PVP) was added to the stripping solution. The structural characteristics of the crystallized products, mainly copper pyrovanadate (volborthite, Cu₃V₂O₇(OH)₂·(H₂O)₂) nanoflakes and nanoflowers and the experimental parameter influencing the efficiency of the stripping process were studied. From the results, the synthesis of nanostructured vanadates is a simple and versatile method for the fabrication of valuable three-dimensional structures providing abundant active zones for energy and catalytic applications.

The textures of the β- and α-phases of the metastable β-titanium alloy Ti5321 after hot deformation were investigated by neutron diffraction. A hot-rolled bar was solutionized in the β-phase field and then hot compressed above and below the β-transus temperature. The initial texture after full recrystallization and grain growth in the β-phase field exhibits a weak cube component {001} and minor {112} and {111} components. After hot compression, a fiber texture is observed, increasing in intensity with compression temperature. Below the β-transus temperature, dynamic recrystallization of the β-phase and dynamic spheroidization of the α-phase interact strongly. The texture of the α-phase is a fiber texture, increasing in intensity with decreasing compression temperature. The mechanisms of texture formation during hot compression are discussed.