Středoevropský technologický institut VUT

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A 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, Ladislav
We 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.
High-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, Jiří
A 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.
High-temperature low-cycle fatigue and fatigue-creep behaviour of Inconel 718 superalloy: Damage and deformation mechanisms
(Elsevier, 2024-09-01) Bartošák, Michal; Horváth, Jakub; Gálíková, Markéta; Slaný, Michal; Šulák, Ivo
In this article, strain -controlled Low -Cycle Fatigue (LCF) and fatigue-creep tests were performed on Inconel 718 nickel -based superalloy at temperatures of 650 degrees C and 730 degrees C. LCF tests at elevated temperatures were performed with a mechanical strain rate of 1 x 10 -3 /s, while fatigue-creep tests involved either tensile or compressive strain dwell. Both the LCF and fatigue-creep tests revealed cyclic softening, with the mean stress evolving oppositely to the applied strain dwell in the fatigue-creep tests. Investigations into the damage mechanisms identified intergranular cracking as the predominant failure mode. Fatigue-creep loading with a compressive dwell resulted in multiple crack initiations from transgranular oxide intrusions, along with multiple creep cavities during loading at 730 degrees C. Deformation features such as persistent slip bands and deformation nanotwins were observed during cycling at 650 degrees C. In addition, fatigue-creep tests at 730 degrees C exhibited 8 phase precipitation and a coarsening of strengthening precipitates, contributing to additional softening that increased over prolonged test durations. Finally, the observed lifetime during LCF tests decreased with increasing temperatures, and fatigue-creep loading was observed to be more damaging than LCF. On the other hand, fatigue-creep loading with a tensile strain dwell demonstrated a higher lifetime compared to LCF at 730 degrees C.
Polypyrrole based Love-Wave sensors devices with enhanced properties to ammonia
(MDPI, 2018-11-23) Šetka, Milena; Král, Zdeněk; Drbohlavová, Jana; Vallejos Vargas, Stella
Love-Wave (LW) sensors based on gas sensoitive polypyrrole (PPy) nanparticles (NPs) and their modification with different gold (Au) loads are developed in this work. The research is focuse on the fabrication process of the gas sensor devices and their snsing properties to ammonia (NH3).
NAND Flash Memory Organization and Operations
(Omics, 2015-06-30) Novotný, Radovan; Kadlec, Jaroslav; Kuchta, Radek
NAND flash memories are well known for their uncomplicated structure, low cost, and high capacity. Their typical characteristics include architecture, sequential reading, and high density. NAND flash memory is a non-volatile type of memory and has low power consumption. The erasing of NAND Flash memory is based on a block-wise base. Since cells in a ash chip will fail after a limited number of writes, limited write endurance is a key characteristic of flash memory. There are many noise causes such as read or program disturbs, retention process, charge leakage, trapping generation, etc. Preferably, all errors in the storage would be adjusted by the ECC algorithm. The conclusion of all mentioned parasitic factors creates a set of external and internal influences which affects variable behaviour of memory in time. To prepare a review of all the important factors that affect the reliability and life-cycle endurance of NAND flash memories and was our main motivation for this paper.

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