PSI - Issue 52

Ivo Šulák et al. / Procedia Structural Integrity 52 (2024) 154–164 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 8. Representative fracture surfaces of the EEQ-111 superalloy cyclically strained at (a) 800 °C; (b ) 900 °C. White arrows indicate the fatigue crack initiation sites; yellow arrows show the fatigue crack propagation direction. 4. Conclusions In this study, the microstructure degradation and high-temperature LCF behaviour of polycrystalline cast nickel based superalloy EEQ-111 were systematically studied. Fatigue performance was compared with IN 713LC and MAR-M247. The main conclusions are as follows: 1) The initial microstructure of EEQ- 111 shows a bimodal distribution of γ ´ precipitates that are stable even after long-term high temperature exposure. The morphology of both cubic and spherical nano-precipitates remains unchanged after fatigue loading at 800 °C. At 900 °C, slight degradation of edges occurs. 2) The initiation of fatigue cracks was exclusively from the surface. The fatigue crack propagation is purely transgranular at 800 °C, whereas a mix of trans granular and intergranular crack propagation is typical at 900 °C . 3) A stable stress response to applied external loading is typical for the low and medium strain amplitudes, whereas cyclic softening occurs in the high strain amplitude domain. 4) The fatigue life of the EEQ-111 superalloy decreases with increasing temperature in Basquin representation. The EEQ-111 superalloy demonstrates the best fatigue performance in comparison with IN 713LC and MAR M247 superalloys. Acknowledgements This work was financially supported by the Technology Agency of the Czech Republic (No. FW03010190). References Agh, A., Amini, A., 2018. Investigation of the stress rupture behavior of GTD-111 superalloy melted by VIM/VAR. Int J Miner Metall Mater 25, 1035 – 1041. https://doi.org/10.1007/s12613-018-1654-z Antolovich, S.D., 2015. Microstructural aspects of fatigue in Ni-base superalloys. Phil. Trans. R. Soc. A. 373, 20140128. https://doi.org/10.1098/rsta.2014.0128 Choe, B.-H., Lee, H.-C., 1995. Cyclic softening and hardening behavior of a nickel-base superalloy. Scripta Metallurgica et Materialia 32, 1283 – 1287. https://doi.org/10.1016/0956-716X(94)00018-D Choi, B.G., Kim, I.S., Kim, D.H., Seo, S.M., Jo, C.Y., 2004. ETA Phase Formation During Thermal Exposure and Its Effect on Mechanical Properties in Ni-Base Superalloy GTD 111, in: Superalloys 2004 (Tenth International Symposium). Presented at the Superalloys, TMS, pp. 163 – 171. https://doi.org/10.7449/2004/Superalloys_2004_163_171 Donachie, M.J., Donachie, S.J., 2002. Superalloys: A Technical Guide, 2nd Edition. ASM International. Gallardo, J.M., Rodr ı́ guez, J.A., Herre ra, E.J., 2002. Failure of gas turbine blades. Wear 252, 264 – 268. https://doi.org/10.1016/S0043 1648(01)00885-7