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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to 800 °C. Unfortunately, the fracture surfaces indicated that the specimen batch used for the fatigue tests at 900 °C possessed larger casting defects. Therefore, the occurrence of the facets on the fractured surfaces was suppressed at several fracture surfaces. and the fatigue crack initiation and propagation were entirely non-crystallographic and perpendicular to the loading direction.

Fig. 3. High-cycle S-N curves of IN 738LC superalloy in comparison with IN 713LC and MAR-M 247 at the temperatures of (a) 800, (b) 900, and (c) 950 °C.

Fig. 4. Fracture surfaces of IN 738LC superalloy specimens after cycling at 800 °C

a) σ a = 300 MPa, N f = 2.8 × 10

5 cycles; b) σ

a = 240 MPa, N f = 1.1 × 10

6 cycles, defect size = 1.4 mm.

A similar appearance of the fracture surface was observed on specimens cycled at 950 °C, see Fig. 6. The same dependence of fatigue crack initiation site on stress level was documented even despite significantly higher influence of environment in the form of pronounced oxidation. Generally, the location of fatigue crack initiation is given by the presence of casting defects at 800, 900, and 950 °C and by stress amplitude magnitude. The surface fatigue crack initiation was characteristic for specimens cycled at higher stress amplitudes, while internal fatigue crack initiation was predominant during the test performed