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- ItemThermal stability of electron beam welded AlCoCrFeNi2.1 alloy(IOP Publishing, 2024-09-30) Rončák, Ján; Jozefovič, Patrik; Müller, Peter; Adam, Ondřej; Judas, Jakub; Dupák, Libor; Zavdoveev, Anatoliy; Jan, Vít; Zobač, MartinAlCoCrFeNi2.1 alloy, which belongs to the group of eutectic high-entropy alloys (EHEAs), possesses a combination of increased strength and ductility. It should retain these properties over a wide temperature range due to the high entropy effect of the system. At the same time, eutectic alloys are generally considered to have good castability, which increases the possibility of casting the alloy in larger volumes. One of the processes, that the alloy does not avoid when applied in industry, are the various joining techniques including electron beam welding. The weld area is often in a non-equilibrium state, which increases the risk of failure during operation. The paper therefore discusses the stability of the microstructure and mechanical properties of AlCoCrFeNi2.1 alloy when exposed to short-term elevated temperatures. The material heated at 900 degrees C for 1 h in a vacuum furnace was observed using light and electron microscopy, analyzed for chemical and phase composition and finally subjected to HV0.1 hardness measurement and tensile strength test. The resulting condition was compared with the welded joint before exposure to elevated temperature. The microstructure of the weld was formed by a fine lamellar eutectic over the entire observed area. EBSD analysis confirmed the presence of a combination of FCC and BCC phases. The material hardness reached an average value of 370 HV0.1. Maximum tensile strength of the weld joint was measured at 944 MPa with the corresponding displacement of the crosshead 6.1 mm. The welded joint demonstrated sufficient stability and the ability to withstand short-term severe elevated temperature conditions.
- ItemMachinability of extruded H13 tool steel: Effect of cutting parameters on cutting forces, surface roughness, microstructure, and residual stresses(Elsevier, 2024-05-19) Kolomý, Štěpán; Malý, Martin; Sedlák, Josef; Zouhar, Jan; Slaný, Martin; Hrabec, Pavel; Kouřil, KarelThe production of H13 tool steel (TS) by material extrusion (MEX) is a promising method in various applications, but as-built surface roughness does not comply with the quality requirements. Hence, this study investigated the effects of cutting parameters on tool wear, cutting forces, surface quality, microhardness, structure, and residual stresses when machining H13 TS produced by MEX. Dry machining (DM) proved advantageous in certain indicators such as tool wear and cutting forces in comparison to the flood cooling (FC). The lowest surface roughness (0.08 mu m) was achieved at the cutting speed of 80 m/min, feed per tooth of 0.005 mm, and FC which corresponded to a 41 % decrease compared to DM under same conditions. Surface microhardness increased by 20 % after machining, decreasing with distance from the surface. The highest compressive residual stresses were observed under FC, while the DM resulted in a 78.2 % decrease in residual stresses due to a partial annealing effect caused by higher surface temperature. Overall, DM exhibited great potential for achieving high-quality surfaces with a favorable structure and residual stresses. This studys novelty and robustness lie in its significant contribution to practical industrial applications, such as mold and core production.
- ItemStructural Phenomena Introduced by Rotary Swaging: A Review(MDPI, 2024-01-18) Kunčická, LenkaRotary swaging is an industrially applicable intensive plastic deformation method. Due to its versatility, it is popular, especially in the automotive industry. Similar to the well-known methods of severe plastic deformation (SPD), rotary swaging imparts high shear strain into the swaged materials and thus introduces grain refinement down to a very fine, even ultra-fine, level. However, contrary to SPD methods, one of the primary characteristics of which is that they retain the shapes and dimensions of the processed sample, rotary swaging enables the imparting of required shapes and dimensions of workpieces (besides introducing structure refinement and the consequent enhancement of properties and performance). Therefore, under optimized conditions, swaging can be used to process workpieces of virtually any metallic material with theoretically any required dimensions. The main aim of this review is to present the principle of the rotary swaging method and its undeniable advantages. The focus is primarily on assessing its pros and cons by evaluating the imparted microstructures.
- ItemThe effect of strain rate and anisotropy on the formability and mechanical behaviour of aluminium alloy 2024-T3(MDPI, 2024-01-13) Harant, Martin; Verleysen, Patricia; Forejt, Milan; Kolomý, ŠtěpánThe present study focuses on the mechanical behaviour and formability of the aluminium alloy 2024-T3 in sheet form with a thickness of 0.8 mm. For this purpose, tensile tests at quasi-static and intermediate strain rates were performed using a universal testing machine, and high strain rate experiments were performed using a split Hopkinson tension bar (SHTB) facility. The material’s anisotropy was investigated by considering seven different specimen orientations relative to the rolling direction. Digital image correlation (DIC) was used to measure specimen deformation. Based on the true stress–strain curves, the alloy exhibited negative strain rate sensitivity (NSRS). Dynamic strain aging (DSA) was investigated as a possible cause. However, neither the strain distribution nor the stress–strain curves gave further indications of the occurrence of DSA. A higher deformation capacity was observed in the high strain rate experiments. The alloy displayed anisotropic mechanical properties. Values of the Lankford coefficient lower than 1, more specifically, varying between 0.45 and 0.87 depending on specimen orientations and strain rate, were found. The hardening exponent was not significantly dependent on specimen orientation and only moderately affected by strain rate. An average value of 0.183 was observed for specimens tested at a quasi-static strain rate. Scanning electron microscopy (SEM) revealed a typical ductile fracture morphology with fine dimples. Dimple sizes were hardly affected by specimen orientation and strain rate.
- 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/).