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- ItemA Comparative Study of the Impact of La2O3 and La2Zr2O7 Dispersions on Molybdenum Microstructure, Mechanical Properties, and Fracture(SPRINGER, 2024-10-23) Tkachenko, Serhii; Slámečka, Karel; Bednaříková, Vendula; Remešová, Michaela; Gejdoš, Pavel; Ksenzova, Olha; Valášek, Daniel; Dvořák, Karel; Šulák, Ivo; Gálíková, Markéta; Baláž, Matej; Deák, Andréa; Cihlář, Jaroslav; Čelko, LadislavWe report, for the first time, the effect of lanthanum zirconate (La2Zr2O7) particles on the microstructure and mechanical behavior of an experimental molybdenum oxide dispersion-strengthened alloy. The focus was on the preparation of the novel Mo-La2Zr2O7 composite using high-energy ball milling and spark plasma sintering and on the comparison of its microstructural and mechanical properties with pure Mo and Mo-La2O3 ODS alloy counterparts. Mechanical properties were assessed using a Vickers hardness test at room temperature and a three-point flexural test in the temperature range from - 150 to 150 degrees C. The microstructure of the studied materials and their fracture behavior were evaluated using x-ray diffraction, energy-dispersive x-ray spectroscopy, and scanning electron and transmission electron microscopy. The strengthening effect of La2Zr2O7 particles was found to be lower than that of La2O3 particles, resulting in a 30-35% lower yield stress and flexural strength of the Mo-La2Zr2O7 alloy compared to the Mo-La2O3 alloy. The experimental Mo-La2Zr2O7 alloy exhibited low plasticity and no distinct ductile-to-brittle transition temperature (DBTT) in the tested temperature range, unlike pure Mo and the Mo-La2O3 alloy, which had the DBTT of 63 and 1 degrees C, respectively. Fracture occurred mainly in a brittle intergranular manner in the entire testing temperature range, while the counterpart materials showed localized plastic stretching at grain boundaries and within grains at and above the transition region. The observed behavior was primarily related to lower strengthening and brittleness as well as less effective grain boundary purification.
- ItemInfluence of Laser Strategies on Performance of Lattice Structures from Magnesium Alloy WE43 Produced by Laser Beam Powder Bed Fusion(WILEY-V C H VERLAG GMBH, 2025-03-05) Jaroš, Jan; Ožvoldík, Daniel; Vaverka, Ondřej; Nopová, Klára; Hurník, Jakub; Zikmund, Tomáš; Kaiser, Jozef; Koutný, DanielLattice structures made of magnesium alloys are perspective for lightweight and biomedical applications. The processing of magnesium alloys and the production of complex geometries is possible with laser beam powder bed fusion. However, the small material volume of the lattice structures and the magnesium alloy require specific process parameters in order to achieve a high quality of the material. Therefore, the influence of two perspective laser strategies (contour strategy and hatch strategy), their combination, and skywriting is investigated. The geometry of the body-centered-cubic (BCC) lattice structure is used, representing the most difficult lattice structure to produce due to the struts inclination. A relative material density of over 99% is achieved with three laser strategies. The laser strategies have a direct influence on the pore distribution, pore shape, and microstructure. All these parameters can influence the mechanical performance of the BCC structures. The best performance is achieved with the hatch strategy with skywriting, which results in a low number of dangerous pores and a fine microstructure. The Young's modulus of material of 40 GPa and the effective elastic modulus of BCC structure of 136 MPa are achieved.
- ItemCarbon fibers decorated with TiO2 nanoparticles for photocatalytic degradation of methylene blue dye(Frontiers Media S.A., 2024-10-23) Chennam, Pavan Kumar; Sepúlveda Sepúlveda, Lina Marcela; Říhová, Martina; Alijani, Mahnaz; Kachlík, Martin; Zazpe Mendioroz, Raúl; Pavliňák, David; Maca, Karel; Macák, JanThis report demonstrates the development of carbon fibers (CFs) decorated with TiO2 nanoparticles (NPs) as an efficient photocatalyst for the photocatalytic degradation of methylene blue (MB) as a model dye. Carbon fibers were produced by carbonization of polyacrylonitrile fibers, previously produced by centrifugal spinning. Subsequently, the CFs were decorated with TiO2 NPs (CFs@TiO2) by tailored soaking protocol using aqueous TiCl4 solution with different concentrations (0.025, 0.05, 0.1, and 0.2 M). SEM analyses revealed that soaking in TiCl4 produced a smooth, conformal, continuous TiO2 nanoparticulate coating with thickness increasing from 40.4 +/- 21.2 to 257.9 +/- 63.9 nm with increasing TiCl4 concentration. X-ray diffraction and Raman spectroscopy confirmed the anatase nature of TiO2. Photocatalytic decomposition rates of MB were assessed under UV light illumination for all CFs@TiO2 samples, and it was revealed that the lowest amount of TiO2 NP on C yielded the highest rates. The synergistic interaction between CFs and TiO2 NPs with a uniform morphology and a well-crystalline anatase structure, present in an optimal amount of fiber bodies, is the key reason for the remarkable photocatalytic performance. This work shows that C fibers decorated with an optimal amount of TiO2 NPs have a great potential as an effective photocatalytic material.
- ItemHigh-Temperature Creep Resistance of FeAlOY ODS Ferritic Alloy(MDPI, 2024-10-01) Dymáček, Petr; Jarý, Milan; Bártková, Denisa; Luptáková, Natália; Gamanov, Štěpán; Bořil, Petr; Georgiev, Vjačeslav; Svoboda, JiříA significant effort in optimizing the chemical composition and powder metallurgical processing led to preparing new-generation ferritic coarse-grained ODS alloys with a high nano-oxide content. The optimization was aimed at high-temperature creep and oxidation resistance at temperatures in the range of 1100-1300 degrees C. An FeAlOY alloy, with the chemical composition Fe-10Al-4Cr-4Y2O3 (wt. %), seems as the most promising one. The consolidation of the alloy is preferably conducted by hot rolling in several steps, followed by static recrystallization for 1 h at 1200 degrees C, which provides a stable coarse-grain microstructure with homogeneous dispersion of nano-oxides. This represents the most cost-effective way of production. Another method of consolidation tested was hot rotary swaging, which also gave promising results. The compression creep testing of the alloy at 1100, 1200, and 1300 degrees C shows excellent creep performance, which is confirmed by the tensile creep tests at 1100 degrees C as well. The potential in such a temperature range is the target for possible applications of the FeAlOY for the pull rods of high-temperature testing machines, gas turbine blades, or furnace fan vanes. The key effort now focuses on expanding the production from laboratory samples to larger industrial pieces.
- ItemUnidirectional propagation of zero-momentum magnons(AIP Publishing, 2024-09-23) Wojewoda, Ondřej; Holobrádek, Jakub; Pavelka, Dominik; Pribytova, Ekaterina; Krčma, Jakub; Klíma, Jan; Panda, Jaganandha; Michalička, Jan; Lednický, Tomáš; Chumak, Andrii V.; Urbánek, MichalWe report on experimental observation of unidirectional propagation of zero-momentum magnons in synthetic antiferromagnet consisting of strained CoFeB/Ru/CoFeB trilayer. Inherent non-reciprocity of spin waves in synthetic antiferromagnets with uniaxial anisotropy results in smooth and monotonous dispersion relation around Gamma point, where the direction of the phase velocity is reversed, while the group velocity direction is conserved. The experimental observation of this phenomenon by intensity-, phase-, and time-resolved Brillouin light scattering microscopy is corroborated by analytical models and micromagnetic simulations.