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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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Fatigue behaviour of nickel base superalloy Inconel 738LC at room temperature
Juliš, M. ; Obrtlík, Karel ; Petrenec, Martin ; Podrábský, T.
Total strain controlled tests have been performed on cylindrical specimens of Inconel 738LC polycrystals at room temperature (23 °C). Cyclic hardening, cyclic stress-strain and fatigue life curves were obtained. Fracture surface was studied using scanning electron microscopy. High amplitude cycling results in early pronounced hardening followed by secondary hardening. Low amplitude cycling is characterized by the stable stress response. Manson-Coffin and Basquin laws can reasonably approximate the fatigue life data. Fatigue crack initiation close to the surface from casting defects is documented.
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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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