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Low cycle fatigue behaviour and fatigue crack initiation in MAR-M247 at 700 °c
Šulák, Ivo ; Obrtlík, Karel ; Hrbáček, K.
The second generation nickel-based superalloy MAR-M247 offersa satisfying combination of fatigue and creep properties and oxidation and corrosion resistance that arerequired for application at elevated temperatures in hostile environments. The microstructure consists mainly oftheface centred cubic γ matrix and ordered γ ́ strengthening precipitates (L12crystal structure). The present work focuses on low cycle fatigue (LCF) behaviour of polycrystalline nickel-based superalloy MAR-M247 at high temperature. LCF tests were conducted on cylindrical specimens in symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 700 °C in ambientair. Cyclic stress-strain curvesand fatigue life curves in the representation ofplastic strain amplitude vs. stress amplitude andstress amplitude vs. the number of cycles to failure, respectively,were plotted and compared with data obtained on Inconel 713LC. Special attention waspaid to the investigation of crack initiation in MAR-M247 during low cycle fatigue. Crack initiation sites were studied by means of scanning electron microscopy (SEM) in dual beam microscope TESCAN LYRA 3 XMU FESEM equipped with focus ion beam (FIB). Specimens’ surface observations revealed the formation of pronounced surface relief indicating localisation of plastic deformation.Observations in transmission electron microscope (TEM)confirmed localisation of cyclic plastic deformation in persistent slip bands along {111} slip planes. Fractographic analysis revealed fatigue crack initiation sites. Fatigue crack propagation in stage I was typical of smooth facets up to 500 μm long.
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LOW CYCLE FATIGUE BEHAVIOR AND FATIGUE CRACK INITIATION IN MAR-M247 AT 700 °C
Šulák, Ivo ; Obrtlík, Karel ; Hrbáček, K.
The second generation nickel-based superalloy MAR-M247 offers a satisfying combination of fatigue and creep properties and oxidation and corrosion resistance that are required for application at elevated temperatures in hostile environments. The microstructure consists mainly of the face centred cubic γ matrix and ordered γ´ strengthening precipitates (L12 crystal structure). The present work focuses on low cycle fatigue (LCF) behaviour of polycrystalline nickel-based superalloy MAR-M247 at high temperature. LCF tests were conducted on cylindrical specimens in a symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 700 °C in ambient air. Cyclic stress-strain curves and fatigue life curves in the representation of plastic strain amplitude vs. stress amplitude and stress amplitude vs. the number of cycles to failure, respectively, were plotted and compared with data obtained on Inconel 713LC. Special attention was paid to the investigation of crack initiation in MAR-M247 during low cycle fatigue. Crack initiation sites were studied by means of scanning electron microscopy (SEM) in dual beam microscope TESCAN LYRA 3 XMU FESEM equipped with focus ion beam (FIB). Specimens’ surface observations revealed the formation of pronounced surface relief indicating localisation of plastic deformation. Observations in transmission electron microscope (TEM) confirmed localisation of cyclic plastic deformation in persistent slip bands along {111} slip planes. Fractographic analysis revealed fatigue crack initiation sites. Fatigue crack propagation in stage I was typical of smooth facets up to 500 μm long.
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Fatigue Crack Initiation in Nickel-Based Superalloy MAR-M247 at High Temperature
Šulák, Ivo ; Obrtlík, Karel
The present work is focused on the study of crack initiation during low cycle fatigue (LCF) loading of the second generation nickel-based superalloy MAR-M247 treated with hot isostatic pressing. LCF tests were conducted on cylindrical specimens in symmetrical push-pull cycle under strain control with constant total strain amplitude and strain rate at 800 °C in air atmosphere. Selected specimens were electrolytically polished to facilitate surface relief observations. Crack initiation sites were studied by means of scanning electron microscopy (SEM) in dual beam microscope TESCAN LYRA 3 XMU FESEM equipped with focus ion beam (FIB). The microstructure of the material is characterised by coarse dendritic grains with numerous carbides and small casting defects. The average grain size was 2.1 ± 0.3 mm. Fractographic analysis revealed the fatigue crack initiation sites and their relation to the casting defects and material microstructure. Casting defects, carbide inclusions and interdendritic areas were found to be important crack nucleation sites. Specimens’ surface observations revealed the formation of pronounced surface relief with short worm-like markings. Fatigue crack initiation in these places is documented and discussed.
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Influence of AlCr Layer to Fatiague Properties of Nickel Superalloy IN 713LC at the Temperature 800°C
Šulák, Ivo ; Julišová, Martina (referee) ; Podrábský, Tomáš (advisor)
The present diploma thesis is focused on the effect of AlCr layer on the low cycle fatigue behaviour of cast polycrystalline superalloy IN713LC at 800°C. Protective layer is made by chemical vapour deposition followed by heat treatment. Fatigue tests were conducted in strain control mode with constant total strain amplitude and strain rate. The fatigue behaviour is assessed by cyclic hardening/softening curves, cyclic stress-strain curves, Manson-Coffin curves and Basquin curves. Microstructure was observed in as-received state and also after cyclic loading by means of optical microscopy and SEM.
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Thermomechanical fatigue of nickel-based superalloys
Pech, Filip ; Škorík, Viktor (referee) ; Šulák, Ivo (advisor)
The main objective of present bachelor thesis is to compile literature review of thermomechanical fatigue of nickel-based superalloys. Superalloys were developed to work at high temperatures, where sufficiently high strength, oxidation resistance, creep resistance, and resistance to other high temperature adverse effects have to be ensured. Superalloys are despite efforts to find alternatives still widely used and therefore it is necessary to know their properties and limitations. The present review compiles basic overview of nickel-based superalloys based on specialized publications. First of all, classification of Ni-based superalloys, chemical composition, along with an overview of the most important phases, which are affecting properties of superalloys were studied in detail. The second chapter describes basics of isothermal fatigue of materials, its definition, description of mechanism and basic fatigue life curves. Penultimate chapter of this literature review deals with thermomechanical fatigue and the structure of text is similar to chapter about isothermal fatigue. In the last chapter is given an overview of thermomechanical fatigue of different types of nickel-based superalloys.
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Influence of input material on technology and production of deep drawn product
Černá, Monika ; Peterková, Eva (referee) ; Šulák, Ivo (advisor)
This bachelor thesis was elaborated in cooperation with company ITW Pronovia, s.r.o within the scope of the bachelor degree and presents an assessment of the effect of material properties and manufacturing technology of a deep-drawn product. In this work the mechanical and technological tests were carried out on the supplied material HT179. This material is further processed into a cartridge for an airbag deployment. During production many defects occurred, especially after cutting out the holes of deep-drawn product. The company established these defects as material property. Therefore it is necessary to evaluate the characteristics of different material sets.
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Influence of Al and AlSi Layer to Fatiague Properties of Nickel Superalloy IN 713LC at the Temperature 800°C
Šulák, Ivo ; Juliš, Martin (referee) ; Podrábský, Tomáš (advisor)
Nickel based superalloys are mainly used for high-temperature applications in energetic and aerospace industry. They are exposed to extremely aggressive environment at high temperature with interaction between fatigue and creep processes, oxidation and erosion. Application of protective surface coating is the right way how to increase the lifetime while increasing performance of machine. Theme of this bachelor’s thesis is to investigate the fatigue parameters of superalloy In713LC at 800 °C and the comparison of these parameters between materials with a protective coating based on Al or Al-Si and material without coating.
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Thermo-mechanical and isothermal fatigue behavior of austenitic stainless steel AISI 316L
Škorík, Viktor ; Šulák, Ivo ; Obrtlík, Karel ; Polák, Jaroslav
Many structural components of nuclear power plant systems are made of austenitic stainless steels. These structures undergo degradation by thermo-mechanical fatigue (TMF) caused by simultaneous cyclic straining and temperature cycling, particularly during start-up, shut-down and transient operations. The present work reports the cyclic deformation behavior and fatigue damage of austenitic stainless steel AISI 316L during TMF and isothermal fatigue (IF) testing in air. Total strain controlled in-phase TMF loading in the temperature range 200 - 600 °C and isothermal fatigue (IF) at 600 °C were performed. Hardening/softening curves, cyclic stress-strain response and fatigue life diagrams were obtained both for TMF and IF tests. Fatigue damage was documented using surface relief and fracture surface observations. Mean stress evolution and fatigue degradation data are employed to discuss the fatigue behavior of 316L steel both in TMF and IF regimes.
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Effect of grit blasting surface treatment on high temperature low cycle fatigue life of Inconel 713LC
Šulák, Ivo ; Obrtlík, Karel ; Čelko, L. ; Gejdoš, P.
This paper presents the results of high temperature low cycle fatigue tests carried out on Inconel 713LC. This polycrystalline nickel based superalloys is mainly used for high temperature applications such as disks, blades and vanes of gas turbine engines. These machine components are manufactured by investment casting and undergo a series of postcast processes to remove remnants of shells, oxides and other contaminants. Grit blasting is one of the most widely used and cheapest technology ensuring adequate cleaning of the surface and at the same time is used to treat the substrate surface prior to application of metalic bond coat and various protective coatings (like diffusion, overlay or thermall barier coatings). Low cycle fatigue tests were conducted on as-received and grit blasted material in fully reversed pull-push cycle in strain control mode with constant total strain amplitude and strain rate at 900 °C in air. Experimental data on fatigue life were evaluated and parameters of Baquin and Coffin-Manson curves were obtained for both tested materials. Specimen surface and cross sections of both treated and untreated materials were analysed prior to fatigue tests and also after testing by means of optical microscopy (OM), as well as scaning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) and Vickers microhardness was measured. Fatigue degradation mechanisms was documented in both materials and negligible effect of grit blasting on low cycle parameters was discussed.
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EFFECT OF HIP ON LOW CYCLE FATIGUE OF MAR-M247 AT 900°C
Šulák, Ivo ; Obrtlík, Karel ; Škorík, Viktor ; Hrbáček, K.
Polycrystalline nickel-base superalloy MAR-M247 is used for high temperature applications requiring excellent combination of fatigue properties, creep resistance and surface stability. These superior high temperature characteristics derive from the microstructure which habitually consists of face centred cubic matrix γ and precipitate γ´ (L12 type ordered structure). In the present work, the high temperature low cycle fatigue behaviour of cast nickel-base superalloy MAR-M247 in as received condition and in hot isostatically pressed (HIP) condition was studied. The microstructure of the materials is characterized by dendritic grains, carbides and casting defects. Distribution and size of defects in both materials were studied. Isothermal low cycle fatigue (LCF) tests were performed on cylindrical specimens under total strain control at 900°C in air. Cyclic stress–strain response and fatigue life of both materials were assessed. Beneficial effects of HIP process on cyclic stress-strain and fatigue life curves are discussed.
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