PSI - Issue 43

Vít Horník et al. / Procedia Structural Integrity 43 (2023) 136–141 Author name / Structural Integrity Procedia 00 (2022) 000 – 000

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propagation in stage I regime can be characterized by two categories. Whereas in a higher level of stress amplitude, the facets were largest and from the surface (due to surface fatigue crack initiation), in a lower level of stress amplitude the facets were localized in the fish eye area only (due to internal fatigue crack initiation). An elevation of the testing temperature resulted in the elimination of the facets (900 and 950 °C). The stage II crack propagation was observed in and outside of the fish eye, depending on the testing temperature. Stage II crack propagation becomes more significant with increasing testing temperature due to the thermally activated processes such as diffusion and climb of dislocations. This phenomenon was reported in several studies on MAR- M 247 superalloy, e.g. Šmíd et al. (2016), or other different alloys, e.g. MacLachlan and Knowles (2001), Pollock and Tin (2006), Pineau and Antolovich (2009). 4. Conclusions The high-cycle fatigue properties of IN 738LC were experimentally determined under symmetrical cyclic loading at temperatures of 800, 900, and 950 °C. The fatigue crack initiation occurred in the interior of all fractured specimens loaded in the lower level of stress amplitudes, while the surface fatigue crack initiation was observed in the higher stress amplitudes. The scatter of the obtained fatigue was caused by casting defects. The elimination of defect size and frequency would lead to pronounced increase of fatigue performance and decrease in data scatter. The stage I regime fatigue crack propagation, characterized by facets, was observed only on fracture surfaces of specimens cycled at 800 °C. Fatigue crack propagation in non-crystallographic stage II regime was typical for fatigue tests at 900 and 950 °C. The fatigue limit of 200 MPa was determined at 800 °C . The decrease in the fatigue performance of IN 738LC with the temperature increase to 900 and 950 °C was documented by fatigue limits of 170 and 150 MPa, respectively. Acknowledgements This research was financially supported by the project FW03010190 of the Technology Agency of the Czech Republic. The base research infrastructure IPMinfra was used for the experimental work. References Kunz, L., Lukáš, P., Konečná, R., Fintová, S., 2012. Casting defects and high temperature fatigue life of in 713LC superalloy . International Journal of Fatigue 41, 47-51. MacLachlan, D. W., Knowles, D. M., 2001. Fatigue behaviour and lifing of two single crystal superalloys. Fatigue and Fracture of Engineering Materials and Structures. 24(8): p. 503-521. Pineau, A., Antolovich, S.D., 2009. High temperature fatigue of nickel-base superalloys – A review with special emphasis on deformation modes and oxidation. Engineering Failure Analysis 16, 2668-2697. Pollock, T.M., Tin, S., 2006. Nickel-based superalloys for advanced turbine engines: chemistry, microstructure and properties. Journal of Propulsion and Power 22, 361-374. Reed, R.C., 2008. The Superalloys: Fundamentals and Applications. Cambridge University Press. Šmíd, M., Horník, V., Hutař, P., Hrbáček K., Kunz, L., 2016. High Cycle Fatigue Damage Mechanisms of MAR -M 247 Superalloy at High Temperatures. Trans Indian Inst. Met. 69, 393 – 397. Š m í d, M., Huta ř, P., Horní k, V., Hrb áč ek, K., Kunz, L., 2016. Stage I fatigue cracking in MAR-M 247 superalloy at elevated temperatures, 21st European Conference on Fracture, (Ecf21), pp. 3018-3025. (b) Šmíd M, Horník V, Kunz L, Hrbáček K, Hutař P. , 2020. High Cycle Fatigue Data Transferability of MAR-M 247 Superalloy from Separately Cast Specimens to Real Gas Turbine Blade. Metals. 10(11):1460.