The article presents the results of an experimental study on the spectral modes of coherent Cherenkov diffraction radiation in the sub-terahertz frequency range. A long cylindrical Teflon radiator was used as a target. The Advanced Research Electron Accelerator Laboratory linear accelerator, located at the Center for the Advancement of Natural Discoveries using Light Emission Synchrotron Research Institute in Yerevan, has been used as a source of electrons with the energy of 3.6 MeV. The radiation was analysed with Martin-Pupplett interferometer and recorded using full band Schottky barrier diode detectors, designed for frequency bands Q: 33-50 GHz, E: 60-90 GHz, and F: 90-140 GHz. The obtained results are compared with theoretical calculations and demonstrated a good consistency. Cherenkov diffraction radiation offers considerable potential for the development of intense photon sources in the THz and sub-THz frequency ranges, as well as for applications in particle beam diagnostics.
A seven-cation layered double hydroxide with the composition MgNiCoAlFeYGd was obtained by soft mechanochemical synthesis followed by hydrothermal treatment. The crystal phase purity of the sample was confirmed by X-ray diffraction, and the unit cell parameters were calculated. Sorption and UV-photocatalytic properties were studied using the model dye methyl orange (MO). Oxidative properties were evaluated using the 3,3′,5,5′-tetramethylbenzidine (TMB) test. The valence state of cobalt was investigated by X-ray absorption near edge spectroscopy (XANES). The synthesized sample demonstrated oxidative activity toward TMB, as well as photocatalytic and sorption activity toward MO. According to the obtained results, cobalt contained in the sample is partially oxidized to the +3 oxidation state, which remains stable after the TMB test.
This study investigated the effect of Si additions (0-35 at.%) on the phase structure, mechanical properties, and oxidation behaviour of a refractory NbTiZr complex concentrated alloy (RCCA). Si promoted the formation of silicide phases (M5Si3-type), transforming the microstructure from a single-phase body-centered cubic (bcc) structure to hypoeutectic bcc + eutectic bcc/M5Si3 and further to a hypereutectic M5Si3 + eutectic M5Si3/bcc mixture. Si significantly enhanced yield strength across a wide temperature range (22-1000 degrees C), but at the expense of room-temperature compressive plasticity and fracture toughness, which decreased as the volume fraction of silicides increased. Oxidation resistance at 1000 degrees C was substantially improved with increasing Si content, reducing mass gain and shifting oxidation kinetics towards more protective regimes. This study highlighted the potential of strategic Si alloying to tailor the properties of NbTiZr-based RCCAs for high-temperature applications.
Tempered martensite embrittlement (TME) limits the feasible range of tempering conditions for high-strength steels. Silicon alloying has proven effective in suppressing TME. However, the quantitative interplay between the concurrent microstructural processes and the evolution of mechanical properties, particularly impact toughness, has not been fully decoupled. This study investigates the microstructural evolution and mechanical response of a high-silicon (1.85 wt%) 0.33C steel during isothermal tempering at 350 degrees C over more than four orders of magnitude in tempering time (20 s to 166.7 h). Using complementary characterization techniques (TEM, XRD, EBSD), a series of distinct microstructural changes is identified: rapid stress relaxation and precipitation of fine fl-Fe2C at early tempering; subsequent gradual carbon enrichment and decomposition of retained austenite (RA); and finally, the replacement of fl-Fe2C by grain boundary cementite. A non-monotonic evolution of Charpy impact toughness, peaking at 28 J after 600 s before declining to 7 J after prolonged tempering, is observed. Kinetic modeling, combining precipitation kinetics and carbon redistribution analysis, demonstrates that the toughness peak is governed by rapid stress relief and carbon stabilization of RA films, which is kinetically retarded by competing fl-Fe2C precipitation in martensite. The subsequent embrittlement is directly correlated with the silicon-retarded decomposition of RA, rather than carbide coarsening or the fl-Fe2C -> cementite transition. The combined multi-technique characterization and kinetic modeling thus delineate, in a time-resolved manner, how competing carbon redistribution processes and carbide transformations control the microstructural pathway leading to TME in a medium-carbon, high-silicon steel.
