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. 7. Microstructural degradation of the EEQ- 111 superalloy tested at 900 °C (a) γ´ morphology after fatigue (ε a = 0.19 %); (b) thin oxide scale with subsurface γ´ depleted zone (ε a = 0.19 %); (c) typical fatigue crack (ε a = 0.70 %); (d) corresponding EBSD map to (c).

Fig. 8 shows the representative fracture surfaces. The initiation of the principal fatigue crack in both cases proceeded from the surface and then propagated semi-elliptically across the specimen. In neither case was initiation from or near the casting defects observed. The hot isostatic pressing process reduced the amount and size of casting defects to a minimum. This diminishes the detrimental notch effect. Fatigue life is thus effectively prolonged (Šulák et al., 2014; Yu et al., 2022; Zhang et al., 2016).