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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.
- ItemModeling Mechanical Properties of Titanium Scaffolds with Variable Microporosity(WILEY-V C H VERLAG GMBH, 2024-10-01) Slámečka, Karel; Skalka, Petr; Pokluda, JaroslavThe article introduces a two-level finite element model for metallic scaffolds with porosity at both design and material levels. Despite several additive manufacturing methods producing structures with controlled hierarchical porosity, their functional properties remain largely unknown, hindering industrial utilization. This article examines how material microporosity affects the mechanical properties of a scaffold prepared by direct ink writing from pure titanium with dimensions typical for orthopedic implants. The study focuses on the compressive response of scaffolds with microporosity ranging from 0.05 to 0.65. The article demonstrates the practical application of the model by estimating the effective Young's modulus and the relative length of the fatigue crack initiation stage. Tensile plastic strains at critical sites exhibit a delocalization from around micropores followed by relocalization into thinning interpore walls with increasing microporosity, resulting in the highest fracture strain predicted for microporosities between 0.2 and 0.3. These strains enable the estimation of the length of the fatigue crack initiation stage, which proves to be very short for all microporosities. This emphasizes the crucial role of the crack growth stage in scaffold fatigue life and confirms the potential for additional experiments on scaffolds with microporosities exceeding 0.15 to enhance their fatigue resistance. The article presents a finite element model for metallic scaffolds, investigating the impact of material microporosity on mechanical behavior. Specifically, the study investigates regular microporous titanium scaffolds prepared by direct ink writing, highlighting the effects of strain delocalization and relocalization on fracture strain. Moreover, the model estimates the relative length of the fatigue crack initiation stage in these materials.image (c) 2024 WILEY-VCH GmbH
- 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.
- ItemComputed tomographic visualisation and 2D/3D microscopic evaluation of soil macro- and micromorphology(CZECH ACADEMY AGRICULTURAL SCIENCES, 2024-10-13) Pospíšilová, Ľubica; Plíšková, Jana; Jaques, Victory; Zikmund, Tomáš; Sedlák, Luboš; Eichmeier, Aleš; Klement, Aleš; Kodešová, Radka; Borůvka, Luboš; Kaiser, Jozef; Menšík, LadislavSoil organic matter and pores distribution within aggregates were studied using X-ray computed tomography (XCT; Nikon XT H 225ST and GE Phoenix L240) and advanced 2D/3D measurements by the digital Keyence VHX-6000 microscope (Japan). A new methodological approach with computed tomography involvement for studying the spatial arrangement of pores, porosity, and soil morphology is presented. Changes in studied parameters are documented along the transect of intensively used Haplic Chernozem. Soil disturbance due to erosion and colluvial soil profile formation is reported. Moreover, soil organic matter quality and aggregate stability were evaluated. Obtained results showed statistically significant differences between the control and eroded sites and between eroded and accumulated sites. The correlation coefficients were the highest for soil organic carbon (SOC) and humic substances C-HS (r = 0.805) and C-HS and C-HA/C-FA (r = 0.764). The highest porosity, aggregates stability and coefficients stability were confirmed on the eroded site. The computed tomography measurements also document the high disturbance of Haplic Chernozem on the control site and the newly formed profile of Colluvisol. Despite excellent complementary technique further research is necessary to improve micro-XCT resolution and capacity for the soil micromorphological study.
- ItemStatistical behaviour of laser-induced plasma and its complementary characteristic signals(Royal Society of Chemistry, 2024-09-04) Buday, Jakub; Holub, Daniel; Pořízka, Pavel; Kaiser, JozefIn this work, we present a study aimed at the statistical distribution of characteristic signals of laser-induced plasmas. This work mainly focuses on observing statistical distribution for repetitive measurement of spectra, plasma plume imaging, and sound intensity. These were captured by using various laser irradiances, spanning between 1.72 and 6.25 GW cm2 for a 266 nm laser. Their distributions were fitted by Gaussian, generalized extreme value (GEV), and Burr distributions, as typical representation models used in LIBS. These were compared using the Kolmogorov–Smirnov (KS) test by its null hypothesis on whether these models are suitable or fail to describe the statistical distribution of the data. The behavior of the data distribution has shown a certain connection to the plasma plume temperature. This was observed for all the used ablation energies. Performances of the statistical models were further compared in the outlier filtering process, where the relative standard deviation of the filtered data was observed. The results presented in this work suggest that an appropriate selection of a statistical model for the data representation can lead to an improvement in the LIBS performance.