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- ItemMechanisms of plastic deformation and fracture in coarse grained Fe-10Al-4Cr-4Y2O3 ODS nanocomposite at 20-1300°C(Elsevier, 2023-05-01) Gamanov, Štěpán; Luptáková, Natália; Bořil, Petr; Jarý, Milan; Mašek, Bohuslav; Dymáček, Petr; Svoboda, JiříThe coarse-grained Fe-10Al-4Cr-4Y2O3ODS nanocomposite (denoted as FeAlOY) has been developed by the authors and shows promising potential for high-temperature structural applications at 1000-1300 & DEG;C. Compared to classical ODS alloys, the FeAlOY contains ten times higher volume fraction of the stable Y2O3 nanodispersion, which gives the alloy its high-temperature strength. Furthermore, the high content of Al in the matrix guarantees excellent oxidation resistance. In practice, one can expect that the FeAlOY is loaded in the temperature range of 20-1300 & DEG;C due to intermittent device operation. To ensure a safe operation, it is necessary to determine the tensile strength and ductility of the FeAlOY in the whole temperature range and detect the dominant mechanisms of strengthening, plastic deformation, and fracture in the characteristic temperature ranges. Above 1100 & DEG;C the FeAlOY reaches ultimate tensile strength of 100 MPa and plasticity of 1%. However, in the temperature range of 400-600 & DEG;C, the plasticity can climb above 40%. The achieved results can also be utilized for the design of the FeAlOY pieces shaping by hot pressing. & COPY; 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
- ItemThe Influence of Foundry Scrap Returns on Chemical Composition and Microstructure Development of AlSi9Cu3 Alloy(MDPI, 2023-05-03) Šmalc, Jan; Vončina, Maja; Mrvar, Primož; Balaško, Tilen; Krutiš, Vladimír; Petrič, MitjaRecycling is now, more than ever, an important part of any foundry process due to the high cost of energy. The basis of the work presented here is a study of the addition of foundry scrap returns to the melt in order to reduce material and energy costs. The most important issue in such a process is the quality of both the prepared melt and final product. In this work, scrap returns were added to the AlSi9Cu3 base alloy in different proportions. Chemical composition was monitored, the solidification path was predicted by CALPHAD calculations and monitored by thermal analysis, and the formed microstructure was studied. The mechanical properties were also determined. The results showed that as the amount of scrap returns increased, elements such as Fe, Ni, Pb, Sr, etc. were more built up and elements such as Mg, Mn, Cr, etc. were decreased due to oxidation. The different chemical composition led to a reduced Mn:Fe ratio, resulting in the formation of needle-like Fe-rich phases and a decrease in mechanical properties.
- ItemChange in Dimensions and Surface Roughness of 42CrMo4 Steel after Nitridation in Plasma and Gas(MDPI, 2022-10-06) Dobrocký, David; Pokorný, Zdeněk; Joska, Zdeněk; Sedlák, Josef; Zouhar, Jan; Majerík, Jozef; Studený, Zbyněk; Procházka, Jiří; Barényi, IgorThe influence of plasma nitriding and gas nitriding processes on the change of surface roughness and dimensional accuracy of 42CrMo4 steel was investigated in this paper. Both processes almost always led to changes in the surface texture. After plasma nitriding, clusters of nitride ions were formed on the surface of steel, while gas nitriding very often led to the new creation of a formation of a “plate-like” surface texture. In both cases of these processes, a compound layer in specific thickness was formed, although the parameters of the processes were chosen with the aim of suppressing it. After the optimizing of nitriding parameters during nitriding processes, it was found that there were no changes in the surface roughness evaluated using the Ra parameter. However, it turned out that when using a multi-parameter evaluation of roughness (the parameters Rz, Rsk and Rku were used), there were presented some changes in roughness due to nitriding processes, which affect the functional behavior of the components. Roughness changes were also detected by evaluating surface roughness profiles, where nitriding led to changes in peak heights and valley depths. Nitriding processes further led to changes in dimensions in the form of an increase of 0.032 mm on average. However, the magnitude of the change has some context on chemical composition of material. A larger increase in dimensions was found with gas nitriding. The change in the degree of IT accuracy is closely related to the change in dimension. For both processes, there was a change of one degree of IT accuracy compared to the ground part (from IT8 to IT9). On the basis of the achieved dimensional accuracy results, a coefficient of change in the degree of accuracy IT was created, which can be used to predict changes in the dimensional accuracy of ground surfaces after nitriding processes in degrees of accuracy IT3–IT10. In this study, a tool for predicting changes in degrees of accuracy of ground parts after nitriding processes is presented.
- ItemPossibilities of reducing the number of welds on rail vehicle doors(Nature Portfolio, 2022-10-07) Sigmund, Marian; Spichal, JanThe paper developed methods that can be employed to reduce the number of welds on a specific rail-vehicle frame door welded from the EN AW 6060 aluminum alloy profiles thermally processed into the T66 state. The profiles were welded by the GTAW method using an S Al 5087 (AlMg4,5MnZr) wire as the filler material. Tensile tests were performed on the supplied samples after welding to check the mechanical properties required. The resulting tensile test data were subsequently used as boundary values for a new design of the door frame having fewer welds. A FEM simulation was carried out using the Virtual Performance Solution software with PAM-Crash extension. The study's biggest achievement was reducing two welds on a real frame door without changing door frame stability. In view of saving welding and producing time and finance by reducing the number of loaded welds. In conclusion, this designed variant is evaluated and tested.
- ItemCutting Force When Machining Hardened Steel and the Surface Roughness Achieved(MDPI, 2022-11-13) Osička, Karel; Zouhar, Jan; Sliwková, Petra; Chladil, JosefThis article deals primarily with the problem of determining the cutting force when machining hardened steels. For this study, the steel used was 100 Cr6, number 1.3505. The secondary aspects of the study focused on the evaluation of the surface quality of machined samples and the recommendation of cutting conditions. A wide variety of components are used in engineering, the final heat treatment of which is hardening. These components are usually critical in a particular product. The quality of these components determines the correct functioning of the entire body of technical equipment, and ultimately, its service life. In our study, these are the core parts of thrust bearings, specifically the rolling elements. The subject of this experiment involves machining these components in the hardened state with cubic boron nitride tools and the continuous measurement of the cutting force using a dynamometer. The machining is carried out on a conventional lathe. A total of 12 combinations of cutting conditions were set. Specifically, for three cutting speeds of 130, 155 and 180 m center dot min(-1), the feed rates of 0.05 and 0.1 mm center dot rev(-1) and the cutting widths of 0.2 and 0.35 mm, were evaluated The evaluation assessed the surface quality by both touch and non-touch methods. A structural equation with the appropriate constants and exponents was then constructed from the data obtained using the dynamometer. The experiment confirmed the potential of achieving a value of the average arithmetic profile deviation Ra in the range of 0.3-0.4 when turning hardened steels with cubic boron nitride.