Microstructure modifications of Al-Si-coated press-hardened steel 22MnB5 by laser welding
Šebestová, Hana; Horník, Petr; Mika, Filip; Mikmeková, Šárka; Ambrož, Ondřej; Mrňa, Libor
2024 - English Weld microstructure depends on the characteristics of welded materials and parameters of welding technology, especially on the heat input that determines the peak temperature and the cooling rate. When the coated sheets are welded, the effect of the chemical composition of the coating must be also considered even though its thickness is only a few tens of microns. During 22MnB5+AlSi laser welding experiments, the ferrite-stabilizing elements of coating modified the weld metal microstructure. Ferrite appeared in a quenched weld metal. The rapid cooling rate accompanying welding with a focused beam limited the homogenization of the weld metal which resulted in the formation of ferritic bands in the regions rich in Si and especially in Al. On the other hand, a high level of homogenization was reached when welding with the defocused beam. The ferritic islands uniformly distributed in the weld metal were formed at 0.4 wt% and 1.6 wt% of Si and Al, respectively. The doubled heat input reduced the Al content to 0.7 wt% insufficient for the ferrite formation at still relatively high cooling rates. Predicting the distribution of ferrite in the weld metal is challenging due to its dependence on various factors, such as cooling rate and the volume of dissolved coating, which may vary with any modifications made to the welding parameters. Keywords: laser welding; high-strength steel; microstructure; heat input; ferrite stabilization Available at various institutes of the ASCR Microstructure modifications of Al-Si-coated press-hardened steel 22MnB5 by laser welding

Weld microstructure depends on the characteristics of welded materials and parameters of welding technology, especially on the heat input that determines the peak temperature and the cooling rate. ...

Šebestová, Hana; Horník, Petr; Mika, Filip; Mikmeková, Šárka; Ambrož, Ondřej; Mrňa, Libor
Ústav přístrojové techniky, 2024

Influence of ball material on the resulting fatigue life of thermal sprayed HVOF coatings in dynamic impact testing
Duliškovič, J.; Daniel, Josef; Houdková, Š.
2024 - English Dynamic impact wear, i.e. contact between two components in the presence of high cyclic local loads, is a challenging failure mode that occurs in many mechanical applications. Many previous studies have confirmed that dynamic impact testing is suitable for evaluating the contact fatigue of thermal sprayed coatings. However, the effect of the test parameters on the resulting lifetime is unclear. The aim of this study describes the effect of the ball material used in the dynamic impact test on the resulting fatigue life of the HVOF thermal sprayed coating. Three test balls made of WC/Co alloy, Si3N4 silicon nitride and 440 C steel were chosen for this study. Dynamic impaction testing was carried out on the Cr3C2-NiCr coating, which was sprayed by HVOF on a 1.2376 high-speed steel substrate. The impact lifetime was described by the number of critical impacts, i.e. the number of impacts before coating fatigue occurs. Furthermore, the depth and volume of impact craters were measured. Using scanning electron microscopy (SEM), the surface of the impacts as well as the microstructure of the coating on the cross-section in the region of the impacts were observed. Furthermore, the mechanism of crack propagation in the coating and the microstructure of the indentor were investigated. Keywords: dynamic impact test; HVOF; Cr3C2-NiCr; fatigue Available at various institutes of the ASCR Influence of ball material on the resulting fatigue life of thermal sprayed HVOF coatings in dynamic impact testing

Dynamic impact wear, i.e. contact between two components in the presence of high cyclic local loads, is a challenging failure mode that occurs in many mechanical applications. Many previous studies ...

Duliškovič, J.; Daniel, Josef; Houdková, Š.
Ústav přístrojové techniky, 2024

Functional Tungsten-based thin films and their characterization
Košelová, Zuzana; Horáková, L.; Sobola, Dinara; Burda, Daniel; Knápek, Alexandr; Fohlerová, Z.
2024 - English Anodizing is a technique by which thin oxide layers can be formed on a surface. Thin oxide layers have been found to be useful in a variety of applications, including emitters of electrons. Tungsten is still a common choice for cold field emitters in commercial microscopy applications. Its suitable quality can be further improved by thin film deposition. Not only the emission characteristic can be improved, but also the emitter operating time can be extended. Tungsten oxide is known for its excellent resistance to corrosion and chemical attack due to its stable crystal structure and strong chemical bonds between tungsten and oxygen atoms. Many techniques with different advantages and disadvantages have been used for this purpose. Anodization was chosen for this work because of the controllable uniform coverage of the material and its easy availability without the need for expensive complex equipment. The anodizing process involves applying an electrical potential to tungsten while it is immersed in an electrolyte solution. This creates a thin layer of tungsten oxide on the surface of the metal. The thickness and properties of the resulting oxide layer can be controlled by adjusting the anodization conditions, such as the electrolyte solution, voltage, and the duration of the process. In this work, H3PO4 was used as the electrolyte to test whether these tungsten oxide layers would be useful for electron emitters, for use in electron guns and other devices that require high-quality electron emitters. The properties were evaluated using appropriate techniques. In general, anodization of tungsten to form thin layers of tungsten oxide layers is a promising technique for producing high quality electron emitters. Keywords: cold-field emission; thin layer deposition; tungsten oxide; resonance enhanced tunneling; anodization Available at various institutes of the ASCR Functional Tungsten-based thin films and their characterization

Anodizing is a technique by which thin oxide layers can be formed on a surface. Thin oxide layers have been found to be useful in a variety of applications, including emitters of electrons. Tungsten ...

Košelová, Zuzana; Horáková, L.; Sobola, Dinara; Burda, Daniel; Knápek, Alexandr; Fohlerová, Z.
Ústav přístrojové techniky, 2024

Surface acoustic wave microfluidic chip for rapid cell sorting
Vejrosta, Jakub; Maňka, Tadeáš; Plichta, Tomáš; Šerý, Mojmír
2023 - English This work revolves around microfluidics and micro-objects manipulation in general. In our device, we are producing surface acoustic wave (SAW). The SAW can be used to sort particles by their size or physical properties and separate them. In medical analysis SAW on microfluidic chip can be used to pre-sorting of body fluids or blood serum for further optical or chemical analysis. The wave is produced by pair of interdigital transducers (IDTs), which are situated on opposite sides of microfluidic channel. As our active material we have used lithium niobate crystalline material for its great piezoelectric properties. This work is also the precursor for measuring the rheological properties of a medium, such as micro-viscosity, via the measurement of the trajectory of a flow trace. Keywords: microfluidics; surface acoustic wave; light microscopy Available at various institutes of the ASCR Surface acoustic wave microfluidic chip for rapid cell sorting

This work revolves around microfluidics and micro-objects manipulation in general. In our device, we are producing surface acoustic wave (SAW). The SAW can be used to sort particles by their size or ...

Vejrosta, Jakub; Maňka, Tadeáš; Plichta, Tomáš; Šerý, Mojmír
Ústav přístrojové techniky, 2023

16th Multinational Congress on Microscopy, 16MCM, 04-09 September 2022, Brno, Czech Republic. Book of abstracts
Krzyžánek, Vladislav; Hrubanová, Kamila; Hozák, Pavel; Müllerová, Ilona; Šlouf, Miroslav
2022 - English Fulltext is available at external website. 16th Multinational Congress on Microscopy, 16MCM, 04-09 September 2022, Brno, Czech Republic. Book of abstracts

Krzyžánek, Vladislav; Hrubanová, Kamila; Hozák, Pavel; Müllerová, Ilona; Šlouf, Miroslav
Ústav přístrojové techniky, 2022

Automation of metallographic sample cleaning process
Čermák, Jan; Ambrož, Ondřej; Jozefovič, Patrik; Mikmeková, Šárka
2022 - English Specimen cleaning and drying are critical processes following any metallographic preparation steps. The paper focuses on automation by reason of absence of the process repeatability during manual sample handling. An etchant or electrolyte results in inhomogeneous surface quality because the solution runs off the specimen surface during its removal from the beaker. High-quality specimen cleaning is absolutely crucial for the acquisition of the specimen suitable for characterization by a scanning electron microscope operated at very low landing energies of the primary electrons (SLEEM). The SLEEM technique is a powerful tool for the characterization of advanced steels, as described by many scientific papers. The SLEEM requires the specimen absolutely free of water and any organic residues on the surface. This work presents a novel unique apparatus enabling automatic specimen cleaning and drying after the etching or electropolishing processes. Automation reduces the influence of dependent variables that would be introduced into the process by the metallographer. These variables include cleaning time, kinematics, and motion dynamics, but the process can also be affected by variables that are not obvious. Performed experiments clearly demonstrate our in-house designed apparatus as a useful tool improving efficiency and consistency of the sample cleaning process. The high quality of the specimen surface is verified using a light optical microscope, an electron scanning microscope, and above mentioned SLEEM technique. Keywords: metallography; sample cleaning; process automation; repeatability Fulltext is available at external website. Automation of metallographic sample cleaning process

Specimen cleaning and drying are critical processes following any metallographic preparation steps. The paper focuses on automation by reason of absence of the process repeatability during manual ...

Čermák, Jan; Ambrož, Ondřej; Jozefovič, Patrik; Mikmeková, Šárka
Ústav přístrojové techniky, 2022

Correction of gradient pulse shape distortions in radial MRI
Vitouš, Jiří
2022 - English This paper focuses on the optimization of gradient-pulse shapes in MRI measurement. The main topic investigated in this paper is optimization of slice-selective gradient, where imperfections may produce phase distortion in the resulting image and also signal loss in the acquired signal. A method for correction is proposed based on the Nelder-Mead algorithm followed by coordinate ascent search in the neighborhood of the found solution. The adjustment is evaluated using a simple Fast low angle shot (FLASH) sequence with radial readout. The results show a significant improvement in the Free induction decay (FID) signal magnitude, echo stability, and an improvement in the homogeneity of image phase. Keywords: MRI; gradient; Nelder–Mead; slice; adjustment Fulltext is available at external website. Correction of gradient pulse shape distortions in radial MRI

This paper focuses on the optimization of gradient-pulse shapes in MRI measurement. The main topic investigated in this paper is optimization of slice-selective gradient, where imperfections may ...

Vitouš, Jiří
Ústav přístrojové techniky, 2022

Gold nanosystems for the detection of molecules using surface-enhanced Raman scatterings (SERS)
Benešová, Markéta
2022 - English Raman spectroscopy is a non-destructive analytical technique to analyze the chemical structure of molecules by a phenomenon known as Raman scattering, which occurs by an inelastic interaction of photons with the valence electrons in molecular bonds. However, Raman scattering can be hard to observe due to other, more frequent phenomena, such as Rayleigh scattering or fluorescence. SERS (surface-enhanced Raman spectroscopy) uses localized surface plasmon resonance (LSPR) of metal nanostructures to amplify Raman scattering. LSPR is a coherent oscillation of conduction electrons that arises from the interaction of electromagnetic radiation with metal nanostructures. The amplification of Raman scattering occurs when the analyte is adsorbed on the surface of such nanostructure and the strong localized electric field interacts with the electrons in its molecular bonds. Signal amplification of several orders of magnitude can be achieved, commonly 103 or more. In our work, we determined the presence of a selected bacterial species by multi-functionalized golden nanoparticles called SERS-tags, which have their surface modified with an antibody and a Raman reporter. The antibody allows the nanoparticles to bind to the surface of a concrete bacterial species based on the antigen-antibody affinity. When the targeted bacterium is covered with the nanoparticles, the Raman reporter signal is amplified by SERS, providing specific and strong Raman response. Therefore, when the Raman reporter signal is detected in a sample, it confirms the presence of the specific bacterium on a single-cell level. Keywords: surface-enhanced Raman spectroscopy; SERS-tag Available at various institutes of the ASCR Gold nanosystems for the detection of molecules using surface-enhanced Raman scatterings (SERS)

Raman spectroscopy is a non-destructive analytical technique to analyze the chemical structure of molecules by a phenomenon known as Raman scattering, which occurs by an inelastic interaction of ...

Benešová, Markéta
Ústav přístrojové techniky, 2022

Unfolded Low-rank + Sparse Reconstruction for MRI
Mokrý, O.; Vitouš, Jiří
2022 - English We apply the methodology of deep unfolding on the problem of reconstruction of DCE-MRI data. The problem is formulated as a convex optimization problem, solvable via the primal-dual splitting algorithm. The unfolding allows for optimal hyperparameter selection for the model. We examine two approaches - with the parameters shared across the layers/iterations, and an adaptive version where the parameters can differ. The results demonstrate that the more complex model can better adapt to the data. Keywords: DCE-MRI; proximal splitting algorithms; deep unfolding; L+S model Fulltext is available at external website. Unfolded Low-rank + Sparse Reconstruction for MRI

We apply the methodology of deep unfolding on the problem of reconstruction of DCE-MRI data. The problem is formulated as a convex optimization problem, solvable via the primal-dual splitting ...

Mokrý, O.; Vitouš, Jiří
Ústav přístrojové techniky, 2022

Effect Of Al2O3 Barrier On The Field Emission Properties Of Tungsten Single-Tip Field Emitters
Burda, Daniel; Knápek, Alexandr
2022 - English This research aims to obtain a more in-depth understanding of the field emission properties of tungsten single-tip field emitters (STFEs) coated with a several tens of nanometer thin barrier of Al2O3. The introduction of an additional barrier into the metal-vacuum interface system of the emitter can be beneficial to improve its performance. The tungsten emitters were prepared using a two-step electrochemical drop-off etching technique. Thin oxide barrier coatings were prepared by using low-temperature atomic layer deposition (ALD), a chemical vapor deposition technique. Field emission was studied in an internally developed field emission microscope (FEM) working in UHV vacuum (< 1·10−7 Pa), and the experimental field emission data were analyzed by the so-called Murphy-Good plotsThe value of the local work function of the grown oxide layer were investigated using Ultra-violet photoelectron spectroscopy (UPS). Keywords: Cold field emission; single-tip field emitters; tungsten tip; aluminum oxide; dielectric coatings; Murphy-Good plot Fulltext is available at external website. Effect Of Al2O3 Barrier On The Field Emission Properties Of Tungsten Single-Tip Field Emitters

This research aims to obtain a more in-depth understanding of the field emission properties of tungsten single-tip field emitters (STFEs) coated with a several tens of nanometer thin barrier of Al2O3. ...

Burda, Daniel; Knápek, Alexandr
Ústav přístrojové techniky, 2022