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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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Low cycle fatigue on Inconel 713L and Inconel 792-5A superalloys at 500 A 700 °C
Petrenec, Martin ; Obrtlík, Karel ; Polák, Jaroslav ; Hrbáček, K. ; Kruml, Tomáš
Cylindrical specimens of cast polycrystalline nickel base superalloys Inconel 713LC and 792-5A were cyclically strained under total strain control at500°C and at700°C.Structural characteristics and morphology of gama´ precipitates of both materials are documented. Dislocations structures were studied using transmission electron microscopy using technique of oriented foils in selected specimens cyclically strained up to failure. Cyclic hardening/softening curves, cyclic stress-strain curves, and fatigue life curves were obtained for both temperatures. 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 relative to structural parameters and to dislocation structures of superalloys studied.
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