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Thermomechanical and Isothermical Fatigue of Surface Treated Nickel Superalloys
Šulák, Ivo ; Pantělejev, Libor (referee) ; Polák, Jaroslav (referee) ; Obrtlík, Karel (advisor)
Yttria-stabilized zirconia-based thermal barrier coating systems are the most widely used commercial coatings in the industry, with practical applications in aircraft engines and land-based power turbines. The purpose of thermal barriers is primarily to protect the substrate from high temperatures and also to increase its oxidation resistance. Currently, concerning the relatively frequent volcanic eruptions and increasing air traffic intensity in desert areas, increased attention is being paid to the development of new thermal and environmental coatings that will withstand the so-called CMAS attack and still successfully meeting the strictest requirements of the aerospace industry. Two newly developed experimental coatings consisting of three successive layers have been developed for this work. The upper two layers are thermal insulating ceramic coatings, where two different uppermost coatings were deposited. The first uppermost layer of the coating is a mixture of mullite and hexacelsian in a ratio of 70/30 wt. %. The second upper most type of coating consists of Al6Si2O13 + MgAl2O4 + BaCO3 in a ratio of 6:3:1 wt. %. The interlayer is made of the commercially utilized yttria-stabilized zirconia. The metallic CoNiCrAlY coating, which is directly deposited on the nickel-based superalloy MAR-M247, fulfils a compensatory function between the mechanical properties of the nickel superalloy and the ceramic coating. The thermal and environmental barrier system was deposited using air plasma spraying (APS) technology. The main objective of this work was to evaluate the effect of the newly developed thermal and environmental barrier coating, which has a high potential for the protection of component surfaces in an aggressive environment, on isothermical and thermomechanical fatigue behaviour of nickel-based superalloy MAR-M247. Low cycle fatigue tests were performed in strain control mode with constant strain amplitude on both uncoated and TEBC coated superalloy. Fatigue hardening/softening curves, cyclic stress-strain curves and fatigue life curves in the representation of total strain amplitude, plastic strain amplitude and stress amplitude on the number of cycles to failure were obtained. Microstructural analysis of MAR-M247 superalloy and a newly developed experimental coating was performed in a scanning electron microscope. The fatigue crack initiation sites were identified and the process of fatigue crack propagation was described. The dislocation arrangement after fatigue loading of MAR-M247 was investigated in a transmission electron microscope. The findings of isothermical and thermomechanical low cycle fatigue behaviour of uncoated and TEBC coated MAR-M247 superalloy and identification of damage mechanisms presented in this dissertation will improve the estimation of safe-life that is particularly relevant to aircraft engines components.
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Thermomechanical and Isothermical Fatigue of Surface Treated Nickel Superalloys
Šulák, Ivo ; Pantělejev, Libor (referee) ; Polák, Jaroslav (referee) ; Obrtlík, Karel (advisor)
Yttria-stabilized zirconia-based thermal barrier coating systems are the most widely used commercial coatings in the industry, with practical applications in aircraft engines and land-based power turbines. The purpose of thermal barriers is primarily to protect the substrate from high temperatures and also to increase its oxidation resistance. Currently, concerning the relatively frequent volcanic eruptions and increasing air traffic intensity in desert areas, increased attention is being paid to the development of new thermal and environmental coatings that will withstand the so-called CMAS attack and still successfully meeting the strictest requirements of the aerospace industry. Two newly developed experimental coatings consisting of three successive layers have been developed for this work. The upper two layers are thermal insulating ceramic coatings, where two different uppermost coatings were deposited. The first uppermost layer of the coating is a mixture of mullite and hexacelsian in a ratio of 70/30 wt. %. The second upper most type of coating consists of Al6Si2O13 + MgAl2O4 + BaCO3 in a ratio of 6:3:1 wt. %. The interlayer is made of the commercially utilized yttria-stabilized zirconia. The metallic CoNiCrAlY coating, which is directly deposited on the nickel-based superalloy MAR-M247, fulfils a compensatory function between the mechanical properties of the nickel superalloy and the ceramic coating. The thermal and environmental barrier system was deposited using air plasma spraying (APS) technology. The main objective of this work was to evaluate the effect of the newly developed thermal and environmental barrier coating, which has a high potential for the protection of component surfaces in an aggressive environment, on isothermical and thermomechanical fatigue behaviour of nickel-based superalloy MAR-M247. Low cycle fatigue tests were performed in strain control mode with constant strain amplitude on both uncoated and TEBC coated superalloy. Fatigue hardening/softening curves, cyclic stress-strain curves and fatigue life curves in the representation of total strain amplitude, plastic strain amplitude and stress amplitude on the number of cycles to failure were obtained. Microstructural analysis of MAR-M247 superalloy and a newly developed experimental coating was performed in a scanning electron microscope. The fatigue crack initiation sites were identified and the process of fatigue crack propagation was described. The dislocation arrangement after fatigue loading of MAR-M247 was investigated in a transmission electron microscope. The findings of isothermical and thermomechanical low cycle fatigue behaviour of uncoated and TEBC coated MAR-M247 superalloy and identification of damage mechanisms presented in this dissertation will improve the estimation of safe-life that is particularly relevant to aircraft engines components.
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Effect of plasma sprayed AlSi coating on low cycle fatigue properties of cast superalloy Inconel 738LC
Obrtlík, Karel ; Pospíšilová, S. ; Juliš, M. ; Čelko, L. ; Podrábský, T.
Air plasma spraying was applied to obtain AlSi protective surface coating on cylindrical specimens of cast polycrystalline superalloy Inconel 738LC. Chemical composition of the surface treated layer was studied and the hardness depth profile was measured. Surface treated and untreated specimens were cyclically strained under total strain control at 800 °C in air. Cyclic stress-strain response and fatigue life of both materials were obtained. The coating results in a slight decrease of cyclic stress-strain curve. A detrimental effect of the surface treatment on derived Wöhler curve is documented while Manson-Coffin curves of both materials are almost identical. Specimen section observations and fracture surface examinations help to discuss fatigue behaviour of both materials.
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Fatigue properties of nickel-base superalloy inconel 792-5A at 800°C
Šmíd, Miroslav ; Obrtlík, Karel ; Petrenec, Martin ; Polák, Jaroslav ; Hrbáček, K.
Smooth specimens were cyclically strained under strain control with constant strain amplitude and constant strain rate. Low cycle fatigue tests were conducted in servo-hydraulic pulsator MTS equipped with a three zone resistance furnace at temperature 800°C in air. Fracture surface was studied in SEM after fatigue test termination. Selected specimens were used to prepare foils for the transmission electron microscope (TEM) observation of microstructure and dislocation arrangement. They were used to obtain cyclic hardening/softening curves, cyclic stress-strain curve and fatigue life curves in the representation of stress amplitude, total strain amplitude and plastic strain amplitude versus number of cycles to fracture. Experimental points can be approximated with the Manson-Coffin law and the Basquin law. Fracture surface examinations revealed fatigue crack initiation sites.
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Comparison of low cycle fatigue characteristics of cast nickel base superalloys Inconel 713 LC a Inconel 792-5A
Petrenec, Martin ; Obrtlík, Karel ; Polák, Jaroslav
Cylindrical specimens of cast polycrystalline nickel base superalloys Inconel 713 LC and Inconel 792-5A were cyclically strained under total strain control at room temperature and at 800 °C. Structural characteristics of both materials are documented. Metallographic observations revealed coarse grains with dendrites, shrinkage pores and carbide inclusions. TEM observation shows differences in the morphology of ordered γ´ precipitates in both materials. Cyclic hardening/softening curves, cyclic stress-strain curves, and fatigue life curves were obtained for both temperatures. The cyclic hardening/softening curves depend both on temperature and plastic strain amplitude. The cyclic stress-strain curves can be approximated by power law. Experimental points of fatigue life curves satisfy the Manson-Coffin and Basquin law. Stress-strain response and fatigue life characteristics are compared at both temperatures and discussed in relation to structural parameters of materials studied.
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