TY - JOUR U1 - Zeitschriftenartikel, wissenschaftlich - begutachtet (reviewed) A1 - Schlesinger, Michael A1 - Schweizer, Christoph A1 - Brontfeyn, Yakiv T1 - Einflüsse auf das thermomechanische Ermüdungsrisswachstum der Nickellegierung Alloy 617 JF - Materials Testing - Materialprüfung N2 - The following contribution deals with the experimental investigation and theoretical evaluation of fatigue crack growth under isothermal and non-isothermal conditions at the nickel alloy 617. The microstructure and mechanical properties of alloy 617 are influenced significantly by the thermal heat treatment and the following thermal exposure in service. Hence, a solution annealed and a long-time service exposed material condition is studied. The crack growth measurement is carried out by using an alternate current potential drop system, which is integrated into a thermomechanical fatigue (TMF) test facility. The measured fatigue crack growth rates results in a function of material condition, temperature and load waveform. Furthermore, the results of the non-isothermal tests depend on the phase between thermal and mechanical load (in-phase, out-of-phase). A fracture mechanic based, time dependent model is upgraded by an approach to consider environmental effects, where almost all model parameters represent directly measureable values. A consistent description of all results and a good correlation with the experimental data can be achieved. N2 - Der vorliegende Beitrag behandelt eine experimentelle Untersuchung und theoretische Bewertung des Ermüdungsrisswachstums unter isothermen und nicht-isothermen Bedingungen an der Nickellegierung Alloy 617. Die Mikrostruktur und die mechanischen Eigenschaften der Nickellegierung Alloy 617 hängen stark von der Wärmebehandlung und der nachfolgenden thermischen Beanspruchung im Betrieb ab. Die Untersuchungen werden daher an einem lösungsgeglühten Ausgangszustand sowie an einer zuvor im Kraftwerksbetrieb langzeitausgelagerten Variante durchgeführt. Die Messung des Risswachstums erfolgt mit einer Wechselstrompotentialsonde, die in einen TMF-Prüfstand integriert ist. Die gemessenen Ermüdungsriss-Wachstumsraten hängen vom Werkstoffzustand, der Prüftemperatur, sowie der Form des Belastungszyklus ab. Bei anisothermer Belastung ergibt sich außerdem eine Abhängigkeit von der Phasenbeziehung zwischen mechanischer Belastung und Temperatur (in-phase, out-of-phase). Ein bruchmechanisch-basiertes zeitabhängiges Modell wurde um einen Ansatz zur Berücksichtigung der umgebungsbedingten Beschleunigung des Risswachstums aufgewertet, wobei nahezu alle Modellparameter direkt messbare Kennwerte darstellen. Es kann mit dem vorgeschlagenen Ansatz eine konsistente Beschreibung aller Versuche und eine gute Korrelation mit den experimentellen Daten erreicht werden. KW - Materialermüdung KW - Thermomechanik KW - Nickellegierung Y1 - 2015 SN - 0025-5300 SS - 0025-5300 U6 - https://dx.doi.org/10.3139/120.110684 DO - https://dx.doi.org/10.3139/120.110684 VL - 57 IS - 2 SP - 131 EP - 135 PB - Hanser ER - TY - JOUR U1 - Zeitschriftenartikel, wissenschaftlich - begutachtet (reviewed) A1 - Schlesinger, Michael A1 - Seifert, Thomas A1 - Preussner, Johannes T1 - Experimental investigation of the time and temperature dependent growth of fatigue cracks in Inconel 718 and mechanism based lifetime prediction JF - International Journal of Fatigue N2 - The following contribution deals with the growth of cracks in low-cycle fatigue (LCF) and thermomechanical fatigue (TMF) tested specimens of Inconel 718 measured by using the replica method. The specimens are loaded with different strain rates. The material shows a significantly higher crack growth rate if the strain rate is decreased. Electron backscatter diffraction (EBSD) is adopted to identify the failure mechanism and the misorientation relationship of failed grain boundaries in secondary cracks. The analyzed cracks propagated mainly transgranular but also intergranular failure can be observed in some areas. It is found that grain boundaries with coincidence site lattice (CSL) boundary structure are generally less susceptible for intergranular failure than grain boundaries with random misorientation. For modeling the experimentally identified crack behavior an existing model for fatigue crack growth based on the mechanism of time dependent elastic–plastic crack tip blunting is enhanced to describe environmental effects based on the mechanism of oxygen diffusion at the crack tip. For the diffusion process the temperature dependent parabolic diffusion law is assumed. As a result, the time dependent cyclic crack tip opening displacement (DCTOD) is used as representative value to describe both mechanisms. Thus, most of the included model parameters characterize the deformation behavior of the material and can be determined by independent material tests. With the determined material properties, the proposed model describes the experimentally measured crack growth curves very well. The model is validated based on predictions of the number of cycles to failure of LCF as well as in-phase and out-of-phase TMF tests in the temperature range between room temperature and 650 °C. KW - Ermüdung KW - Schädigung KW - Oxidation KW - Rissausbreitung Y1 - 2017 UR - http://www.sciencedirect.com/science/article/pii/S0142112316304224 SN - 0142-1123 SS - 0142-1123 U6 - https://dx.doi.org/10.1016/j.ijfatigue.2016.12.015 DO - https://dx.doi.org/10.1016/j.ijfatigue.2016.12.015 VL - 99 IS - Part 2 SP - 242 EP - 249 ER -