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NANOSTRUCTURE CHARACTERIZATION OF IN738LC SUPERALLOY FATIGUED AT HIGH TEMPERATURE
Petrenec, M. ; Strunz, Pavel ; Gasser, U. ; Heczko, Milan ; Zálešák, J. ; Polák, Jaroslav
The nanostructure of Inconel 738LC Ni-superalloy strengthened by trimodal Y precipitates distribution was investigated after Low Cycle Fatigue (LFC) loading at temperature 700°C. Different microscopic techniques as Scanning Electron Microscope (SEM) equipped with STEM detectro, transmission Kikuchi diffraction in the SEM, transmission electron microscope (TEM) in the bright field mode and high resolution transmission electron mciroscopes (HRTEM) in STEM mode were used for the characterization and quantification of superalloy nanostructure. The characteristic morphology of y precipitates was examined by ex-situ and in-situ Small Angle Neutron Scattering (SANS) at high temperatures. All adopted microscopic techniques indicate that the morphology of y precipitates distributed in the y matrix as recived state corresponds to two types, i.e. large cuboid-like precipitates with the size around 670 nm, and the spherical precipitates with the diameter 52nm. After eh LCF tests at temperature 700°C, the ex-situ SANS measurement yielded addititonal scattering intensities coming from another small y precipitetes with estimated size up to 10nm.
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NANOSTRUCTURE CHARACTERIZATION OF IN738LC SUPERALLOY FATIGUED AT HIGH TEMPERATURE
Petrenec, M. ; Strunz, Pavel ; Gasser, U. ; Heczko, Milan ; Zálešák, J. ; Polák, Jaroslav
The nanostructure of Inconel 738LC Ni-superalloy strengthened by trimodal γ’ precipitates distribution was investigated after Low Cycle Fatigue (LCF) loading at temperature 700°C. Different microscopic techniques as Scanning Electron Microscope (SEM) equipped with STEM detector, transmission Kikuchi diffraction in the SEM, transmission electron microscope (TEM) in the bright field mode and high resolution transmission electron microscopes in STEM mode were used for the characterization of nanostructure. The characteristic morphology of γ’ precipitates was examined by ex-situ and in-situ Small Angle Neutron Scattering (SANS) at high temperatures. All microscopic techniques indicate that the morphology of γ’ precipitates distributed in the γ matrix as received state corresponds to two types, i.e. large cuboid-like precipitates with the size around 670 nm, and the spherical precipitates with the diameter 52 nm. After the LCF tests at temperature 700°C, the ex-situ SANS measurement yielded additional scattering intensities coming from another small γ’ precipitates with estimated size up to 10 nm.
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Analysis of cyclic plasticity of fatigued nickel based superalloys at elevated temperatures
Petrenec, Martin ; Tobiáš, Jiří ; Polák, Jaroslav ; Šmíd, Miroslav ; Chlupová, Alice ; Petráš, Roman
Cyclic strain controlled multiple step tests have been performed on cylindrical specimens of cast Inconel 738LC superalloy at 23 and 800 °C and Inconel 792-5A superalloy at 800 °C in laboratory atmosphere. The effect of temperature on the cyclic stress-strain response characterized by internal and effective cyclic stress components and on the dislocation arrangement has been studied. The evolution of the effective and internal stress components and effective elastic moduli were derived from the hysteresis loops analyzed according to the statistical theory of the hysteresis loop. Cyclic hardening/softening curves and shortened cyclic stress-strain curves were obtained at all temperatures in both superalloys. The shortened cyclic stress-strain curves (CSSCs) can be fitted by power law at all temperatures and for both materials. They are shifted to lower stresses with increasing temperature. The CSSC of Inconel 792-5A is shifted to higher stress amplitude in comparison with that of Inconel 738LC due to different number and type of precipitates. Observation of dislocation structures by TEM revealed cyclic strain localization into persistent slip bands. Cyclic stress-strain response is compared at all temperatures in both superalloys and discussed in relation to the changes of internal and effective stress components and microstructural parameters of the material. Higher stress response of the Inconel 792-5A than of the Inconel 738LC superalloy at 800°C is due to higher effective stresses of respective γ´ phases.
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Low Cycle Fatigue and Analysis of the Cyclic Stress-strain Response in Superalloy Inconel 738LC
Tobiáš, Jiří ; Chlupová, Alice ; Petrenec, Martin ; Polák, Jaroslav
The paper describes the results of fatigue behavior study on cast polycrystalline nickel based superalloy tested at 23 and 800 °C. Cylindrical specimens of Inconel 738LC were cyclically strained under total strain control to fracture and multiple step tests were performed to study the effect of temperature on the internal and effective cyclic stress components. Fatigue life curves were approximated by the Manson- Coffin and Basquin laws. The resulting curves were shifted to lower fatigue lives with increasing temperature. The evolution of the effective and internal stress components and effective elastic modules were derived from the hysteresis loops which were analyzed according to the statistical theory of hysteresis loop. Cyclic stress-strain response at both temperatures and the changes of internal and effective stress components were discussed in relation to microstructural parameters of the superalloy.
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Microstructure Characterization and Faigue Behavior of Beta Phase Containing Gama-TiAl Alloy
Petrenec, Martin ; Beran, Přemysl ; Šmíd, Miroslav ; Chlupová, Alice ; Kuběnová, Monika
The microstructure and fatigue properties of Ti–44Al–7.8Nb – 0.2Ni (at.%) alloy after graded cooling heat treatment were investigated. Different techniques as SEM, TEM and FIB were used for characterization of microstructure. Quantification of phase volume fraction was measured by neutron diffraction method. After graded cooling heat treatment the structure consists of fully lamellar uniform grains which contain lamellar phases /2 and cubic phases (ordered B2 and disordered phases) at grain boundary and interlamellar spaces. The foils for TEM were prepared using FIB technique and observed in TEM in order to identify B2 phase by selected electron diffraction. Low cycle fatigue behaviour at 750 °C shows stable fatigue crack propagation due the presence of plastic beta and B2 phases.
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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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Effect of heat treatments with a pointed cooling on the mechanical compression properties of TiAl intermetalic
Petrenec, Martin ; Kruml, Tomáš ; Zemanová, Adéla ; Krahula, Karel
The influence of the graded cooling heat treatments on a change in the structure and the room temperature mechanical compression properties of cast Ti-44Al-8Nb intermetallic were studied. The coolings were the air cooling and the graded cooling which was composed of combination of furnace cooling and air cooling for selected two temperatures 1315 °C and 1200 °C. These selected temperatures were used from the measuring of the differential thermal analysis (DTA). All heat treatments used remold the cast nearly lamellar structure ?/?2 to the fully lamellar uniform structure and decreased the average grain size to the half. The air cooling and the graded cooling with temperature 1315 °C were produced in higher yield stress and lower plasticity due the very thin lamellar thickness and planar grain boundary. While higher plasticity and lower yield stress are obtained using the graded cooling with temperature 1200 °C. It is caused by the very thick lamellar spacing and locked grain boundaries.
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Fatigue life and fatigue fracture of nickel-based superalloy Inconel 792-5A at room and at elevated temperatures
Šmíd, Miroslav ; Obrtlík, Karel ; Petrenec, Martin ; Polák, Jaroslav ; Hrbáček, K.
The aim of the present work is to study the effect of temperature on the fatigue life and fracture in cast polycrystalline nickel base superalloy Inconel 792-5A. Surface relief and fracture surface observations help to elucidate fatigue damage mechanism in the material used to produce the most critical component of gas turbines. Fatigue live curves can by approximated by the Manson-Coffin and Basquin law. Special attention was paid to the cyclic strain localisation on the specimen surface. Specimens strained with different strain amplitudes were used for fractographic investigation at each temperature. Both, the surface relief and the fracture surface observations, provide data on fatigue crack initiation. Detailed study of fracture surface topography was performed at all temperatures and different strain amplitudes and typical morphologies are documented. Fatigue damage mechanisms and crack path are discussed in relation to temperature, strain amplitude and crack lenght.
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Nízkocyklová únava tvárné litiny s 2,8 % niklu
Tesařová, H. ; Petrenec, Martin ; Pacal, B. ; Musilová, I.
Cast ductile iron with the ferritic matrix alloying with 2.8% Ni was subjected to cycling with constant strain amplitudes and the cyclic stress-strain response and fatigue life were studied experimentally. The original microstructure is documented using light microscope. Fracture surface was studied using scanning electron microscopy. Manson-Coffin and Basquin laws can reasonably approximate the fatigue life data. Fatigue crack initiation from shrinkage cavity is documented.
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