PSI - Issue 52

ScienceDirect Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2022) 000 – 000 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2022) 000 – 000 Available online at www.sciencedirect.com Procedia Structural Integrity 52 (2024) 154–164

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2452-3216 © 2023 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Professor Ferri Aliabadi 10.1016/j.prostr.2023.12.016 2452-3216 © 2023 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Professor Ferri Aliabadi 2452-3216 © 2023 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Professor Ferri Aliabadi * Corresponding author. Tel.: +420-532-290-343 E-mail address: sulak@ipm.cz © 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of Professor Ferri Aliabadi Abstract The material under investigation was polycrystal line Sulzer’s nickel -based superalloy EEQ-111 which is equivalent to the original GTD-111 developed in the late 1970s. The EEQ-111 superalloy is typical with coarse polyhedral dendritic grains with an average grain size of (2.48 ± 0.87) mm. The microstructure consists of γ channels, a bimodal distribution of nano - sized coherent γ´ precipitates, γ/γ´ eutectic, and MC and M 23 C 6 carbides. The proportion of casting defects in the material is minimal due to the application of hot isostatic pressing. Low cycle fatigue experiments were executed on solid cylindrical specimens with a gauge length and diameter of 15 mm and 6 mm, respectively. A symmetrical push-pull cycling under strain control mode was utilized at 800 °C and 900 °C using servo -hydraulic testing machine MTS 810. Hysteresis loops, fatigue hardening/softening curves, and fatigue lifetime curves in Coffin-Manson, Basquin, and total strain amplitude representations were obtained. Analysis of fracture surfaces and secondary cracks from metallographic sections revealed the preferential initiation sites of fatigue cracks that are independent of temperature. In contrast, the fatigue crack propagation is purely transgranular at 800 °C, whereas a mix of transgranular and intergranular crack propagation can be found at 900 °C indicating grain boundary weakening. Abstract The material under investigation was polycrystal line Sulzer’s nickel -based superalloy EEQ-111 which is equivalent to the original GTD-111 developed in the late 1970s. The EEQ-111 superalloy is typical with coarse polyhedral dendritic grains with an average grain size of (2.48 ± 0.87) mm. The microstructure consists of γ channels, a bimodal distribution of nano - sized coherent γ´ precipitates, γ/γ´ eutectic, and MC and M 23 C 6 carbides. The proportion of casting defects in the material is minimal due to the application of hot isostatic pressing. Low cycle fatigue experiments were executed on solid cylindrical specimens with a gauge length and diameter of 15 mm and 6 mm, respectively. A symmetrical push-pull cycling under strain control mode was utilized at 800 °C and 900 °C using servo -hydraulic testing machine MTS 810. Hysteresis loops, fatigue hardening/softening curves, and fatigue lifetime curves in Coffin-Manson, Basquin, and total strain amplitude representations were obtained. Analysis of fracture surfaces and secondary cracks from metallographic sections revealed the preferential initiation sites of fatigue cracks that are independent of temperature. In contrast, the fatigue crack propagation is purely transgranular at 800 °C, whereas a mix of transgranular and intergranular crack propagation can be found at 900 °C indicating grain boundary weakening. Keywords: EEQ 111 superalloy; high temperature; cyclic stress-strain behaviour; fatigue lifetime. 1. Introduction Advanced nickel-based superalloy EEQ-111 is an equivalent alloy to the original GTD-111 for application in the first and second stages of gas turbine blades. The employment of nickel-based superalloys in harsh environments of gas turbines is given by their excellent high temperature strength, creep and fatigue performance, and outstanding oxidation resistance (Donachie and Donachie, 2002; Reed, 2008). In particular, the key to the high strength of nickel- Fracture, Damage and Structural Health Monitoring Stress-Strain Response and Fatigue Lifetime of EEQ-111 Superalloy in Cyclic Loading at High Temperatures Ivo Šulák a* , Karel Obrtlík a a Institute of Physics of Materials, The Czech Academy of Sciences, Žižkova 22, 616 00 Brno, Czech Republic Fracture, Damage and Structural Health Monitoring Stress-Strain Response and Fatigue Lifetime of EEQ-111 Superalloy in Cyclic Loading at High Temperatures Ivo Šulák a* , Karel Obrtlík a a Institute of Physics of Materials, The Czech Academy of Sciences, Žižkova 22, 616 00 Brno, Czech Republic Keywords: EEQ 111 superalloy; high temperature; cyclic stress-strain behaviour; fatigue lifetime. 1. Introduction Advanced nickel-based superalloy EEQ-111 is an equivalent alloy to the original GTD-111 for application in the first and second stages of gas turbine blades. The employment of nickel-based superalloys in harsh environments of gas turbines is given by their excellent high temperature strength, creep and fatigue performance, and outstanding oxidation resistance (Donachie and Donachie, 2002; Reed, 2008). In particular, the key to the high strength of nickel- * Corresponding author. Tel.: +420-532-290-343 E-mail address: sulak@ipm.cz