Ústav strojírenské technologie
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- ItemInfluence of Imposed Strain on Weldability of Dievar Alloy(MDPI, 2024-05-14) Izák, Josef; Benč, Marek; Kunčická, Lenka; Opěla, Petr; Kocich, RadimThe presented work is focused on the influence of imposed strain on the weldability of Dievar alloy. Two mechanisms affecting the microstructure and thus imparting changes in the mechanical properties were applied-heat treatment (hardening and tempering), and rotary swaging. The processed workpieces were further subjected to welding with various welding currents. In order to characterize the effects of welding on the microstructure, especially in the heat-affected zone, and determine material stability under elevated temperatures, samples for uniaxial hot compression testing at temperatures from 600 to 900 degrees C, optical and scanning electron microscopy, and microhardness testing were taken. The testing revealed that, although the rotary swaged and heat-treated samples featured comparable microhardness, the strength of the swaged material was approximately twice as high as that of the heat-treated one-specifically 1350 MPa. Furthermore, it was found that the rotary swaged sample exhibited favorable welding behavior when compared to the heat-treated one, when the higher welding current was applied.
- ItemStudy of dynamic behaviour via Taylor anvil test and structure observation of M300 maraging steel fabricated by the selective laser melting method(Elsevier, 2024-07-20) Kolomý, Štěpán; Jopek, Miroslav; Sedlák, Josef; Zouhar, JanThis paper deals with the M300 high strength maraging steel fabricated via selective laser melting method. Mechanical properties especially microhardness and compressive yield strength of maraging steel in as-printed state were observed. The acquired data was implemented in Johnson-Cook constitutive equation used for numeric simulation, which showed the satisfactory correlation with the observed experiment. Dynamic behaviour under high strain rate (impact velocity reached 185 m.s-1)- 1 ) was investigated via Taylor Anvil Test. The experiment revealed structure and geometrical changes accompanied with the creation of characteristic funnellike and cylindrical areas on the deformed sample. Impacted sample forehead featured the increase of micro- hardness (465 HV) accompanied with structure changes. The structure in the funnel-like area exhibited the decrease of average grain size, which reached the minimum (3.1 mu m) in the vicinity of the impacted forehead. Closer analysis revealed that the high strain rate caused the increase of high fraction high-angle grain boundaries (50,8 %) and higher geometrically necessary dislocation density (52.77 1.m-- 2 ) in the funnel-like area.
- ItemCorrosion behavior of selective laser melting-manufactured bio-applicable 316L stainless steel in ionized simulated body fluid(AccScience Publishing, 2024-01-05) Kocich, Radim; Kunčická, Lenka; Benč, Marek; Weiser, Adam; Németh, GergelyAdditive manufacturing (AM) is gaining increasing popularity in various fields, including biomedical engineering. Although AM enables fabrication of tailored components with complex geometries, the manufactured parts typically feature several internal issues, such as unpredictable distribution of residual stress and printing defects. However, these issues can be reduced or eliminated by post-processing via thermomechanical treatment. The study investigated the effects of combinations of AM and post-processing by the intensive plastic deformation method of rotary swaging (variable swaging ratios) on microstructures, residual stress, and corrosion behaviors of AISI 316L stainless steel workpieces; the corrosion tests were performed in an ionized simulated body fluid. The results showed that the gradual swaging process favorably refined the grains and homogenized the grain size. The imposed swaging ratio also directly influenced the development of substructure and dislocations density. A high density of dislocations positively affected the corrosion resistance, whereas annihilation of dislocations and formation of subgrains had a negative effect on the corrosion behavior. The first few swaging passes homogenized the distribution of residual stress within the workpiece and acted toward imparting a predominantly compressive stress state, which also favorably influenced the corrosion behavior. Lastly, the presence of the {111}||swaging direction texture fiber (of a high intensity) increased the resistance to pitting corrosion. Overall, the most favorable corrosion behavior was acquired for the AM sample subjected to the swaging ratio of 0.8, exhibiting a strong fiber texture and a high density of dislocations.
- 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.