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Influence of severe plastic deformation and subsequent annealing on creep behaviour of martensitic 9% Cr steel
Král, Petr ; Dvořák, Jiří ; Sklenička, Václav ; Horita, Z. ; Tokizawa, Y. ; Tang, Y. ; Kunčická, Lenka ; Kuchařová, Květa ; Kvapilová, Marie ; Svobodová, M.
The objective of the study is to evaluate the effects of severe plastic deformation (SPD) and annealing on creep behaviour of advanced tungsten modified creep-resistant 9 % Cr martensitic P92 steel. The as-received P92 steel was deformed by high-pressure torsion (HTP), high-pressure sliding (HPS) and rotary swaging (RS) at room temperature prior creep testing. These SPD methods imposed significantly different equivalent plastic strain in the range from 1 up to 20. Constant load creep tests in tension were performed in an argon atmosphere at 873 K and applied stress ranging from 50 to 200 MPa. The microstructure and phase composition of P92 steel were studied using a scanning electron microscope Tescan Lyra 3 and a transmission electron microscope Jeol 2100F. The results show that under the same creep loading conditions the HPT and HPS-processed P92 steel exhibited significantly faster minimum creep rates, creep fracture strain and the decrease in the value of the stress exponent of the creep rate in comparison with as-received P92 steel. However, it was revealed that the RS-processed specimens exhibited one order of magnitude lower minimum creep rate and lower ductility compared to commercial P92 steel. The creep curves for the HPT and HPS-processed states exhibited a pronounced minimum of strain rate. The pronounced minimum of strain rate disappeared when these states were annealed at 923K/500h before application of creep loading. The microstructure changes occurring during creep and different creep behaviour between as-received and deformed states are discussed.
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Housing production by cold forming
Kouřil, Jakub ; Kunčická, Lenka (referee) ; Jopek, Miroslav (advisor)
The bachelor thesis is focused on the production of a part by cold forming. The subject of the thesis is the design of the technology of production of a housing with a production rate of 6 000 000 pcs/year by extrusion and tamping. The austenitic stainless steel X5CrNi18-10 is used for the production. Based on simulations, the most suitable geometric configuration of the forming operations was selected. The whole production process consists of a first cutting, two forming and a last machining and radnishing operation. Based on the calculated forming force of 175,6 kN and the required power of 425 W, the CHUN ZU CBF-83S automatic forming machine was selected. At the same time, the tool is designed and in the end a techno-economic evaluation is carried out, which also includes the calculation of the piece price considering a 15% profit, which amounts to 1,24 CZK.
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WE43 BIOCOMPATIBLE ALLOY AFTER SEVERE PLASTIC DEFORMATION: STRUCTURE CHARACTERIZATION
Kunčická, Lenka ; Král, Petr ; Dvořák, Jiří ; Kocich, R.
The report presents results of the analyses of biocompatible WE 43 Mg-based alloy processed by friction stir processing (FSP) at two different rotational speeds of 400 RPM, and 1200 RPM. The structures were observed by scanning electron microscopy (SEM), electron backscattered diffraction (EBSD). Observations were primarily focused on characterizations of grains and textures, supplementary testing of mechanical properties was performed via tensile tests. The results of low angle grain boundaries fractions and grain sizes showed that both the processing methods led to significant grain refinement and recrystallization, the average grain diameter within the 1200 RPM sample was less than 2 μm. Texture observations showed slight tendencies of the grains to align in the {0001}〈101̅0〉 and {0001}〈112̅0〉 preferential orientations, however, the maximum intensities were only about two times random. Supplementary tensile tests confirmed the positive effects of FSP on structures and properties of both the samples.
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THE INFLUENCE OF CONSOLIDATION PROCEDURE PARAMETERS ON COMPACTION OF AL POWDER
Lowe, T. C. ; Kunčická, L. ; Kocich, R. ; Davis, C. F. ; Hlaváč, L. ; Dvořák, Jiří
The influence of different consolidation procedures on compaction of Al powders was evaluated. Powder preparation procedures consisted of selection of particle size distribution, cold isostatic pressing (CIP), and vacuum sintering. Processing parameters investigated included the number of compression steps, compression pressure, and sintering temperature and time. Densities of the samples after compression and also after sintering were measured and compared. The overall oxygen content was analysed using by Energy Dispersive Spectroscopy. Phase composition was determined using X-ray. Microhardness measurements were performed to evaluate the degree of compaction. Double-step CIP at 200+300 MPa and subsequent sintering at 500°C for 60 min produced the best combination of properties from all the consolidation technologies of Al particles. Of the particle size ranges studies, those with diameters between 20 and 45 μm produced the best results. Aluminum oxide was present in the structure after all the processing treatments.
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