Papers by Keyword: Electron Microscopy

Abstract: AZ91 magnesium injection molding is suitable for manufacturing complex-shaped electronic product frames or thin plates. However, the strengthening effect of the Mg₁₇Al₁₂ precipitate in AZ91 is limited, and it tends to dissolve during heat treatment, leading to a lack of particles that can pin grain boundaries and prevent grain growth. To address these challenges, the LAZ561Ca alloy has been developed, offering a reduced density (83% of AZ91), AlLi nanoprecipitates with strong strengthening capabilities, and thermally stable Ca-bearing intermetallics that effectively pin grain boundaries, maintaining a fine-grained structure (~8 μm) even after heat treatment. Experimental results demonstrate that AZ91 undergoes abnormal grain growth after solution treatment at 400°C due to a significant reduction in Zener pinning forces. In contrast, the LAZ561Ca alloy, with stable Al₂Ca precipitates, resists such growth during two-stage heat treatment at 370°C – 400°C. Through the coupling between Thermo-Calc and MICRESS software, multiphase field modeling reasonably reproduced the microstructure evolution during injection molding and heat treatment processes, highlighting its value in establishing digital physical metallurgy models. This study reveals the microstructural mechanisms of magnesium alloys, confirming the critical role of Ca-bearing precipitates in grain growth suppression. It provides a foundation for further optimization of alloy compositions and heat treatment conditions, paving the way for advanced magnesium alloys with enhanced performance in injection molding applications.

Abstract: Research and development of materials in the nuclear industry, including the assessment of irradiated components in nuclear power plants, rely heavily on research infrastructures that facilitate the preparation and analysis of radioactive samples. The metallographic preparation of samples must be carried out in shielded, hermetically sealed boxes and hot cells, as a large amount of dusty radioactive particles is released during the sample preparation process. Small samples, thin films for scanning and transmission electron microscopy (SEM, TEM), and powdered samples from biological shielding concretes are prepared in glove boxes, where a constant negative pressure is maintained. The enclosures of the boxes are constructed of thick-walled steel plates to shield against the ionizing radiation emitted by radioactive samples, protecting personnel. Subsequent microscopic analyses allow for the assessment of material degradation in operational nuclear power plant components caused by radiation-induced microstructure damage. These analyses focus both on existing materials, with the aim of extending the lifespan of nuclear power plants, and on newly tested materials irradiated as part of domestic and international programs, including those conducted at research reactors like LVR-15, operated by the Řež Research Center (CVŘ). Different analytical requirements call for the preparation of various types of samples. At CVŘ, X-ray diffraction analysis of powdered samples is primarily used to evaluate structural and phase changes in the cement and aggregate of concrete structures caused by radiation aging, which can impact the overall integrity of the structure. Monitoring these changes and predicting material behavior are essential for evaluating the safety, stability and durability of concrete used in biological shielding, containment structures, spent nuclear fuel storage pools and future deep radioactive waste repositories. Thin films for electron microscopy are prepared specifically to assess detailed changes, such as radiation-induced microstructure damage in reactor internals or fuel cladding, which result in dimensional changes and the degradation of mechanical properties due to neutron radiation.

Abstract: In the presented work the features of formation of metal-fullerene films of the systems Al-C₆₀, Au-C₆₀, Cu-C₆₀, Ti-C₆₀ from atomic-molecular flows in vacuum were investigated, the processes of surface resonance plasmon absorption and diffusion were studied. It is shown that electron microscopy, optical, Auger-electron and X-ray spectroscopy methods are effective for the study of metal-fullerene films. The combination of different methods of spectroscopy and electron microscopy allowed to establish the dependence of the grain size of the films, the shift of the position of the plasmon absorption maximum, diffusion parameters on the ratio of metal and fullerene components, to establish the fact of formation of the chemical compound Cu₆C₆₀.

Abstract: The article describes the conditions for obtaining new thermal insulation materials from the waste of mechanical processing of soft hardwood wood. The recommendations for the production of new resource-saving technologies of gypsum-wood and chip-and-glue composites are justified, which makes it possible to dispose of waste from the processing of soft hardwood wood. It was found that the birch pulp extract, along with cellulose and lignin, contains d-erythrosis, which is easily washed out of the wood with water or a solution of "mineralizer" and gets into the cement dough, which leads to a slowdown in hardening and a decrease in compressive strength. It is shown that the existing technological processes for eliminating the negative influence of saccharides on the strength of wood aggregate composites are complex, requiring multi-stage treatment of the aggregate with various chemicals or long-term exposure. A method based on the use of binders that do not interact with extractable substances, such as gypsum or urea-formaldehyde glue, is proposed. By scanning electron microscopy, it was found that the structure of the gypsum-wood composite varies depending on the sequence of input components. The nature of the effect of microcrystalline cotton cellulose on the change in the physical and mechanical properties of the gypsum-particle composite using cavitation-treated sawdust was revealed and its optimal dosage was determined. The regression dependences of the influence of the consumption of wood chips and glue on the compressive strength of the chip-and-glue composite were obtained by the experimental planning method.

Abstract: The article investigates influence of large plastic deformations created in the Bridgman anvils on the mechanical properties and microstructure of metastable alloys of the iron-chromium-nickel system of the austenitic-martensitic class. It is found that the application of deformation in the Bridgman anvils with a true logarithmic deformation e = 6-7 leads to formation of the α-phase (deformation martensite) with significantly higher mechanical properties compared to martensite formed during deformation by linear rolling. The authors reveal the differences in the microstructure of the alloy after deformation in the Bridgman anvils and deformation by rolling, which explain the discovered effect.

Abstract: The work is devoted to the study of the phenomenon of grain boundary slippage (GBS) in the ARMCO pure iron at the periphery of the laser treatment zone. Using optical metallography and high-resolution scanning electron microscopy (SEM), the characteristic features of the GBS mechanism were revealed: stepped boundaries, accommodation zones, and grain rotation. It was found that under laser irradiation in the heat-affected zone, the plastic deformation of the ferrite matrix is ​​fully realized by the GBS. Slipping of boundaries is carried out under conditions of ultra-high-speed heating of the ferrite matrix not lower than 700 °C, and the degree of deformation by the GBS mechanism does not exceed 5-6%.

Abstract: The work is devoted to the study of the specific features of the structure of vacuum ion-plasma coatings, called by the authors substructural defects. Formed during the deposition of coatings of various compositions by the mechanism of helical growth, these surface crystalline formations, after reaching a certain size, spontaneously extruded (pushed out) from the coating. The cavities (niches) remaining at the site of the defect are filled (healed) by the deposited ions in the process of further growth of the coating. On the basis of thermodynamic analysis, theoretical estimates of the extrusion conditions were obtained in the work, which give a satisfactory agreement between the calculated and experimental data.

Abstract: In order to reduce CO₂ emission and energy consumption, more recycled secondary materials have to be used in foundry industry, especially for Al-Si-Mg based alloys for semi-solid processing. In this paper, Al-Si-Mg based alloys with the addition of recycled secondary materials up to 30 % (10, 20, 30 %, respectively) have been produced by semi-solid processing. The solidification microstructure was investigated using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Furthermore, computed tomography (CT) was also used to elucidate the size, size distribution, number density, volume fraction of porosities. It was found that with the addition of the recycled secondary materials up to 30 %, there is no significant effect on the solidification microstructure in terms of the grain size and the shape factor of primary α-Al and the second α-Al. More importantly, the morphology of eutectic Si can be well modified and that of the Fe-containing phase (π-AlSiMgFe) can be tailored. Furthermore, with increasing recycled secondary materials, at least another two important issues should also be highlighted. Firstly, more TiB₂ particles were observed, which can be due to the addition of Al-Ti-B grain refiners for the grain refinement of recycled secondary materials. Secondly, a significant interaction between Sr and P was also observed in the recycled secondary materials. The present investigation clearly demonstrates that Al-Si-Mg based alloys with the addition of recycled secondary materials at least up to 30% can be used for semi-solid processing, which may facilitate better sustainability.

Abstract: External wooden structures have own place in the building industry for ages. The problem is that wood easily degrades due to UV radiation, atmospheric conditions and biological aggressors. We are trying to eliminate degradable factors by photocatalytic materials (namely titanium oxide). Those materials are efficient UV absorbers and they are able to destroy biological aggressors also. Nowadays, there is no information about the interactions between wooden surface and non-photoactive or photoactive forms of TiO₂. TiO₂ exists in many morphological forms. The planar particles were chosen for the purpose of our research and applied on a wooden surface. The samples of wood (namely pine) were monitored for 255 days and subsequently evaluated using an electron microscope. The use of TiO₂ was compared with reference material and a reference commercial coating.

Abstract: Comparative studies of wear resistance during dry friction of vacuum ion-plasma coatings of nitride systems TiAlN and CrAlSiN are carried out. The structural parameters, coating thickness, and physical and mechanical properties were chosen as comparison parameters. A fundamental difference in the wear mechanisms of the coatings is demonstrated. In the TiAlN-system coatings develop an oxidative wear mechanism due to their insufficient heat resistance. The CrAlSiN-system coatings have maximum resistance to plastic deformation. And they are wear out according to the fatigue mechanism, which is typical for coatings with a high level of mechanical properties.