PSI - Issue 68

Matias Jaskari et al. / Procedia Structural Integrity 68 (2025) 480–485 M. Jaskari et al. / Structural Integrity Procedia 00 (2025) 000–000

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Fig. 3. Inverse pole figure (IPF) map of printed and heat treated In718 in respect of (a) build- and (b) XY-direction, and (c) IPF pole plot showing preferred orientation in <110>-type direction.

3.2. Fatigue Fatigue results are presented as an S-N plot in Fig 4a, and it can be noted how the surface quality optimization by electropolishing increases the fatigue resistance for the whole measured fatigue regime. For example, at 550 MPa stress amplitude the lifetimes for the as built an electropolished samples were 6.8x10 4 and 3.1x10 5 cycles, respectively, indicating a considerable increase in the fatigue resistance in high cycle fatigue (HCF) regime. The FAT50% limit for the as built surface quality sample was 220 MPa, and after electropolishing the limit increased to 420 MPa, showing more than 90% increment in fatigue limit. This indicates that the surface quality has a substantial effect on the fatigue behavior of PBF-LB In718 alloy, and results agree with literature. For example, Rautio et al. (Rautio et al., 2023) measured the fatigue limit of PBF-LB In718 to be 350 and 500 MPa in as built and electropolished condition, respectively, indicating slightly better fatigue behavior than in this study. Further, Witkin et al. and Yamashita et al. (Witkin et al., 2019; Yamashita et al., 2018) conducted similar research for PBF-LB In718, and the fatigue limit of as built samples were also calculated to be roughly 300 MPa with same used stress ratio of -1. Vicker’s indentation hardness was conducted for polished cross-section before and after fatigue at 800 MPa stress amplitude, and it can be noted that some cyclic softening is present after fatigue with high stress amplitude, as is shown in Fig 4b. Although the data here is limited, it agrees with the literature (Sonntag et al., 2024). Measured hardness values were 450 and 436 HV for the sample before and after fatigue, respectively.

Fig. 4. (a) S-N plot of both studied structures and (b) indentation depth vs. indentation load plot before and after fatigue at 800 MPa stress amplitude.