Seznam abstraktů 2023: SEKCE E - NEŽELEZNÉ KOVY A SLITINY

Complex shearing of extruded tube (CSET) is a recently developed technique of severe plastic deformation producing tubes from a bulk billet in one-step-processing. It represents a combination of extrusion and two passes of the type of equal channel angular pressing. Additionally, the sample is further deformed by friction between the rotating mandrel and the tube. In this contribution we describe the changes of the microstructure as well as textures during individual deformation steps of CSET processing of Al single crystal. Electron back scatter diffraction (EBSD) revealed presence of the gradient microstructure from the inner surface and remaining parts of the tube. Simultaneously the texture at the inner surface differs from that in the bulk parts of the tube due to the larger portion of dynamically recrystallized regions. The gradient microstructure is also reflected in measurements of the tube microhardness.

Complex concentrated alloy (CCA) with a nominal composition Al0.4CoCr1.3FeNi1.3(Si,Ti,C,B)0.4 was solidified under two different solidification conditions. As-cast (AC) ingot was prepared by vacuum induction melting in a ceramic crucible followed by centrifugal casting into a graphite mould. Steady-state growth conditions were applied during preparation of directionally solidified (DS) ingot in a Bridgman-type apparatus at a constant growth rate 1.39 x 10-5 ms-1 and constant temperature gradient using a ceramic crucible. Both ingots were subjected to the analysis of the microstructure by light microscopy (LM) and scanning electron microscopy (SEM). The chemical composition of the coexisting phases was measured. Segregation of Al, Si, Ti, B and C to the interdendritic region during solidification results in the formation of several interdendritic phases identified in the ingots. The effect of solidification conditions on the size of dendrites and interdendritic phases was evaluated. Isothermal annealing at 1260°C leads to the melting of all interdendritic phases. Effective partition coefficients of alloying elements were calculated from the measured chemical composition of dendrites and interdendritic region in samples annealed at 1260°C for 1 h followed by water quenching.

Welding of components processed by additive manufacturing (AM) to conventionally produced components become important for industrial applications. Among AM production methods, SLM method provides number of advantages such as use of various type of materials, increased functionality, relatively low cost and the production of smooth surface components ready to use.
Within the scope of this study, preliminary research studies were carried out to demonstrate the feasibility of similar and dissimilar friction stir welding of AlSi10Mg plates produced by selective laser melting. Mechanical performances in terms of tensile and hardness values of simmilar and dissimilar welded joint combinations of AlSi10Mg plates were investigated. In order to determine welding defects, macro/micro structural characterisation was performed on welding zones. It was observed that the density of micro porosities which came from SLM production method were decreased. The tensile strength of similar AlSi10Mg joint was measured higher respect to base metals.

Through the rising amount of hydrogen in natural gases provided by the suppliers technical questions about the process control based on the off-gas composition as well as about the supply of the neces-sary process heat come up. But also the hydrogen solubility plays a significant role in many processes in which solid or liquid metals like copper are produced. This research aims to provide answers to these questions. The changed off-gas composition of the hydrogen enriched natural gas when com-busting in a shaft smelting furnace calculated in this study as well as the changed heat output. As it is important that during the combustion the necessary process heat for the melting of the copper cathodes can be provided or if an additional heat source or a higher volume of input gas is needed. For the modelling of the gas combustion special attention is paid to the components oxygen and carbon monoxide as well as the in the gas atmosphere remaining hydrogen. Based on that the to be expected hydrogen solubili-ty in different copper qualities is modelled in a thermodynamically software solution. The results are compared to other studies which aimed for the hydrogen solubility with a specific look on the depend-ency of hydrogen solubility on oxygen solubility.

High entropy alloys have promising mechanical and functional properties, but their thermomechanical processing at industrial scale is still not possible. One of the reasons is that the processing parameters are mostly unknown. Therefore, we aim to determine the relationships between processing parameters and the microstructure for four hypo-eutectic high entropy alloys. We hot deformed three dual-phase (FCC and BCC phase) alloys, named Al0.41Cr0.47Fe0.46Co0.38NiTi0.01, Al0.39Cr0.44Fe0.44Co0.38NiTi0.01, Al0.42Cr0.45Fe0.46Co0.41Ni, and one single FCC-phase alloy Al0.24Cr0.43Fe0.46Co0.41Ni at temperatures between 1000 and 1100°C. The compression tests consist of single-stage compression, strain rate jumps, multistage holding and deformation cycles. Additionally we performed pre-and post-heat treatments. We observed dynamic recrystallization of the single-FCC phase alloy after slow single-stage compression, under a strain rate jump and at multistage tests. This alloy also recrystallizes statically during annealing. On the other hand, the dual-phase materials did not dynamically recrystallize notably during deformation, and partially recrystallize during annealing. Only the dual-phase alloy with an initial finely lamellar BCC-phase (Al0.42Cr0.45Fe0.46Co0.41Ni) showed significant recrystallization during hot compression. The recrystallization kinetics slows down drastically by the pinning effect of the BCC-phase on the grain boundaries. Futhermore, the BCC-phase globularizes if its thickness is small. With this study we determine thermomechanical treatment parameters for the grain refinement, and explain the role of the BCC-phase on the restoration mechanisms.

The metallurgical industry is characterized by significant consumption of material and energy resources. The natural resources used are primarily non-renewable. The hydrometallurgical zinc extraction is distinguished by a variety of processes and equipment, possible options for replacing some of them with more efficient ones, opportunities for maximum utilization of energy resources. The object of the present analysis is the actually functioning chemical-technological system - KCM - SA, Plovdiv. The plant is the largest zinc and lead producer in Southeast Europe. The fundamental production units, namely roasting of zinc sulphide concentrates, sulphuric acid leaching of the obtained calcine, electrowinning of zinc, ecologically oriented units - processing SO2 - containing gases to sulfuric acid and waste zinc cakes via Waelz process, as well as the system as a whole, have been analysed. The exergy method of thermodynamic analysis was applied as a research method. The obtained results are compared with those from our previous studies, as well as with literature data on similar processes. Higher energy-technological efficiency and reduction of the harmful impact on the environment can be achieved by increasing the share of renewable energy resources and processed secondary raw materials and reducing specific energy consumption.

Inconel 718 additively manufactured by direct metal deposition (3DMD) was tested for stress-strain, fatigue crack growth resistance and fracture toughness. A subsequent EBSD study and instrumented indentation tests were carried out to explain the observed behaviour. All of the above properties are strongly influenced by the texture of the as-deposited material and the resulting low modulus of elasticity. In contrast, instrumented indentation modulus was close to that of conventionally produced In 718. However, the observed anisotropy of fracture toughness and fatigue crack growth rate is rather low in the three perpendicular directions tested. After hot isostatic pressing, the texture disappears and the elastic properties approach those of conventionally produced In718. Furthermore, the fracture properties are significantly improved after HIP.

Metallic nanoparticles are of great interest because of their special electronic, catalytic, optical, and magnetic properties that are often controlled by their characteristic dimension. For example, ferromagnetic materials like nickel are the size of a single-domain structure. Ni nanoparticles with a size of ~ 10 nm could be prepared by gas aggregation technique. Their subjection to elevated temperatures during subsequent post-processing could result in their unfavorable coagulation and sintering, resulting in a degeneration of their functionality. The behavior and stability of Ni nanoparticles at elevated temperatures were studied by in-situ heating in TEM and compared with simulation using molecular dynamics calculations.

Currently, an avalanche of technology development can be observed in the world, which results in an increase in the production and sale of electrical and electronic devices. The lifetime of electronic components, which at the end of the 20^th century was 4 to 6 years, was shortened to 2 years in the first decade of the 21^st century, and even to 9 months in the case of mobile phones. Today, most electrical and electronic devices contain printed circuit boards (PCB). On the one hand, a printed circuit board with electronic components is a hazardous waste due to the content of toxic components (Cr, Pb, Be, Hg, Cd, Zn, Ni), on the other hand, it is a source of many valuable elements, including precious metals (e.g. Au, Ag, Pt, Cu), non-ferrous metals (Sn, Ni, Cr, Zn, Sb, In, Pb), rare earth metals (Ta, Ge), platinum group metals, as well as iron and silicon.
The metals in PCBs can be present in much higher concentrations than in conventional ore deposits, making PCB waste a particularly interesting material for recycling.
PCB recycling involves multiple steps using a combination of physical, chemical, thermal and metallurgical processes. The main methods of recovering metals from PCBs are pyrometallurgical and hydrometallurgical methods. Hydrometallurgical techniques largely involve acid leaching, which is the most common leaching method today and has many advantages including high leaching rate and fast kinetics, but is quite corrosive. In laboratory tests, mineral acids such as H2SO4, HNO3, HCl, as well as aqua regia are used for leaching. Additionally, oxidants in the form of O2, O3, Cl2, H2O2, Fe2(SO4)3 (Fe3+), FeCl3, NaCl, CuSO4 (Cu2+) are used. The article will review interesting and effective methods of leaching printed circuit boards from used mobile phones in the context of recovering copper and other metals contained in this waste.

Because of a limited source of germanium and its high demand caused by growing technology industry, secondary sources become attractive and suited alternatives. In the present paper copper slag containing germanium was used as source and aluminothermic reduction was adopted as mode of reduction. To achieve the recovery of germanium from fayalitic slag, characterization of the as received copper slag, effect of varying basicity on Ge recovery and feasibility of Ge recovery through off-gas, effect of varying aluminium amount on Ge recovery at 1350°C for a two and half hours residence time were investigated. A bench scale furnace was used for smelting. The characterization techniques of the raw slag included XRF, XRD, SEM-EDX, and AAS. Products were characterized using same techniques except XRF. The obtained results were analysed using statistical tools. Results showed that the slag was amorphous, predominantly fayalitic with the presence of low amount of magnetite. The highest recoveries of germanium in the metal increased significantly with slight increase of both the basicity and aluminium. The same behaviour was observed when the aluminium amounts was increasing, the recoveries seemed to have been increasing significantly.

This work deals with the development of the preparation route for the composites with nickel aluminide reinforced by FeSi particles. The optimization of mechanical alloying of individual phases, mixing and consolidation by spark plasma sintering is presented. The composite is developed for the application as a future tool material.

In this study, Ni Coated Si3N4 powders were produced by mixing homogeneously with commercially used Astaloy Cr-M powders and sintering in a neutral gas environment at 1000-1400°C in a tube furnace. The microstructure and mechanical properties of the produced samples were investigated. Si3N4 powders are coated with Electroless Nickel coating technique before sintering. The phases formed were determined by X-ray analysis after sintering. Ni-coated Si3N4 and matrix phase Astaloy Cr-M commercial casting powders are reinforced with ceramic phase to make them resistant to friction. XRD, SEM (Scanning Electron Microscope) analyzes were made and characterized on the produced composite. The best hardness value of 86.12 HB was obtained in the composite sample produced from 10%Si3N4-Astaloy Cr-M)%10Ni composition at 1400°C.

We have performed a multi-methodological theoretical study of impact of thermal vibrations on the Mössbauer effect in the tetragonal beta-phase of tin. We have seamlessly combined (i) atomic-scale numerical data in the form of mean square displacements of Sn atoms determined by quantum-mechanical calculations, (ii) continuum-level thermodynamic modeling based on the quasi-harmonic approximation and (iii) theoretical analysis of Mössbauer effect resulting in the prediction of temperature dependence of Mössbauer factor. The computed results were compared with our Mössbauer and X-ray experimental data. We show that classical theoretical approaches based on simplistic Debye model of thermal vibrations of solids can be nowadays replaced by exact
ab initio calculations of individual thermal vibrations. While both Debye and our approach slightly deviate from the experimental data, our suggested methodology bears promises for future improvement and a better agreement with measurements, i.e. the prospect that the over-simplified Debye model may not offer. For details see M. Friák et al., Computational Materials Science 215 (2022) 111780, https://doi.org/10.1016/j.commatsci.2022.111780. ACKNOWLEDGEMENTS: The authors acknowledge the Czech Science Foundation for the financial support received under the Project No. 22-05801S. Computational resources were provided by the Ministry of Education, Youth and Sports of the Czech Republic under the Projects e-INFRA CZ (ID:90140) at the IT4Innovations National Supercomputing Center and e-Infrastruktura CZ (e-INFRA LM2018140) at the MetaCentrum as well as CERIT Scientific Cloud, all provided within the program Projects of Large Research, Development and Innovations Infrastructures.

Tin pest is a term for modification from white tin to grey tin, which leads to degradation of tin or tin-rich alloys. The most common alloying elements present in historical organ-pipes are Pb, Cu and Fe. The influence of individual alloying elements has not been reliably described, yet. Not only on the concentration of the alloying element but also on the distribution may play the important role. In dependence on heat-treatment, the Cu and Fe can be in the Sn matrix present in these forms: i) as large intermetallic particles after casting (Cu6Sn5 or FeSn2), ii) as solid solution after homogenization annealing and iii) as fine precipitates after ageing. The microstructure of model alloys and real historical organ-pipes samples and the degradation mechanism will be described.
The authors acknowledge the Czech Science Foundation for the financial support received under the Project No. 22-05801S.

Thermoelectric generators represent a unique way for recovering waste heat. Modules are made from specialized materials with thermoelectric properties. They represent cost-effective, simple, easy to maintain and reversible solution to handling any wasteful energy in the form of heat. Modules consist of many N and P semiconductor pairs connected in a series. These devices are very flexible and can be used as heaters, coolers or generators based on Peltier’s and Seebeck’s effects. With careful material selection it is possible to enforce or reduce the desired effect. The main disadvantage of thermoelectric modules is their low conversion efficiency. However, novel materials with significantly improved efficiency sparked renewed interest in these materials from scientific and commercial sectors. New and reliable procedure to measure thermoelectric properties, mainly Seebeck’s coefficient and electrical conductivity, is introduced in this submission. Our solution is cost-effective and easily reproducible because it is made from readily available and 3D printed parts. Our method uses a significant amount of calibration materials to achieve accuracy in wide range values for room temperature measurements. Materials based on SnSe alloy represent an ideal material for constructing thermoelectric modules and are characterized in this submission. Even low amounts of other elements used as dopants can significantly change physical properties of these alloys. It is even possible to get N and P type semiconductors using the same dopant with varying concentration. Both materials therefore have similar mechanical properties in a wide temperature range. Efficiency of these materials is adequate for typical thermoelectric materials.

Two main characteristics of a thin film defining many film properties are film thickness and grain size. Film hardness, electrical conductivity, and film stress evolution are all related to the size of constituent grains. Both thickness and grain size are firmly connected and depend on the deposition technique. A standard method to prepare nanocrystalline thin films of different thicknesses is via physical vapor deposition, where the columnar character of the deposited grains is typical. As a result, grain size is increased with film thickness. A way to alter the grain size while the film thickness remains constant is via recrystallization and grain growth during heat treatment. Al-based 50 nm thick films were prepared by DC magnetron sputtering onto a dissolvable surface. Free-standing films were prepared, and their microstructure was characterized in the transmission electron microscope (TEM). The preferential orientation of grains was analyzed by Automated phase and orientation mapping equipped in TEM (ACOM-TEM). The films were then annealed in situ in TEM to monitor the structural changes and recrystallization mechanisms. The experimental procedure was then simulated by molecular dynamics (MD), where the parameters such as grain size and orientation can be precisely controlled, and the results were compared.

The article presents the most important casting defects arising at the interface of the diffusion connection between the iron ring insert and the casting of the piston made of silumin. The dynamic development of internal combustion engines has led to an increased demand for engine pistons with a cast-iron insert which is designed to reinforce the top part of the piston. The connection of the cast iron insert and the piston made of silumin is realized by the alfining process. It has been found that these defects occur most often during the alfining process of inserts in Al-Si alloy, (so-called AS9). The quality parameters of the bimetallic layer were determined on the basis of the metallographic criterion of material standards. A number of solutions were proposed for the introduction of alloying additives into the bath to neutralize unfavorable iron-based phases and change their morphology. During the analysis of the alfining process, AS9 alloy whose chemical composition changes as the process proceeds was studied. The study presents the chemical composition, iron growth in the alfin bath, analyses of material structure, porosity, intermetallic phases and other parameters relevant to the process. Porosity, resulting from gaseous impurities in the AS9 alloy, and other casting defects, examples of which are presented in the form of macro- and microstructures, were also found in the area of the diffusion interface between the insert and the piston. The main research directions for reducing the presented defects are also given.

The high carbon ferromanganese process produces an alloy saturated with carbon. The alloy contains Mn metal, Fe and C. Carbon dissolves into the alloy, and therefore it is important to calculate the activity of manganese in the alloy. Data dealing with the solubility of carbon in liquid ferroalloy are available but only applied to specific melts. Because the dissolution of carbon into the manganese alloy was not as obvious as in steel production, the behaviour of carbon in steel production was considered the archetype and became the accepted tradition in the manganese alloy production. The assumption was considered because of the solubility of carbon in liquid. Mn, Fe and Mn-Fe present similarities in their interaction parameters. In this investigation, two different equations linear regression that are used in the steel production were tested to establish their validity when using a basic manganese ore. The deviations of the experimental carbon solubility values obtained in this study are narrow such that the fitting of the model albeit revisited but strongly reconducted and cautiously adopted, therefore not reviewed. Therefore, Turkdogan’s (1956) and Tuset and Sandvik’s (1970) thermodynamic predictions on the carbon solubility in Mn-Fe melt remain valid and reliable for the production of high carbon ferromanganese using any of the Nchwaning ores.