PSI - Issue 75

John Hock Lye Pang et al. / Procedia Structural Integrity 75 (2025) 29–34 Author name / Structural Integrity Procedia (2025)

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As shown in Figure 5, the Sequence 2 processed specimen displayed uneven surface profiles resulting from plastic deformation due to shot peening. This process introduced compressive residual stress, which enhances fatigue resistance when compared to the specimen that underwent only HIP and surface machining. The areal average roughness (Sa) of the Sequence 2 processed specimen was measured at 4.50 μm, whereas for the Sequence 1 processed specimen, it was only 0.26 μm . The results demonstrate that the sequential post-treatment method incorporating shot peening modifies the crack initiation mechanism through beneficial surface plastic deformation, thus further improving the fatigue performance of LPBF-processed 316L stainless steel. 4. Conclusions This study evaluated the effectiveness of applying two sequential post-treatment methods to improve fatigue performance of LPBF-processed 316L stainless steel specimens. The two post-treatment sequences both started with HIP and surface machining, while Sequence 2 includes an additional step of shot peening. Both sequences were experimentally validated as effective in enhancing fatigue performance compared to the as-built condition, with Sequence 2 demonstrating a greater extension of fatigue life. Fractographic analysis indicated a shift in crack initiation from surface regions in Sequence 1 to subsurface regions in Sequence 2, attributed to shot peening. Surface profile analysis indicated that shot peening induced beneficial plastic deformation, delaying crack initiation and suppressing surface crack propagation, consistent with the findings from fractographic analysis and fatigue testing. These results indicate that sequential post-treatment of HIP, surface machining, and shot peening can effectively improve the fatigue performance of LPBF-processed 316L stainless steel by modifying crack initiation mechanisms, building upon internal pore closure and surface irregularity removal achieved through HIP and surface machining. Acknowledgements The authors would like to acknowledge that this research work is supported by The RIE2025 Manufacturing, Trade and Connectivity (MTC) Industry Alignment fund Pre-Positioning (MTC-IAF-PP) Grant No. M24N2a0018. The Lead PI, John H. L. PANG would like to thank the School of Mechanical and Aerospace Engineering and Nanyang Technological University, Singapore for providing research support for the MTC-IAF-PP projects. References [1 ] K.A. Shiyas, et al., A review on post processing techniques of additively manufactured metal parts for improving the material properties, Mater. Today Proc. 46 (2021) 1429 - 1436, https://doi.org/10.1016/j.matpr.2021.03.016. [ 2] M. Anand, et al., Issues in fabrication of 3D components through DMLS Technique: A review, Opt. Laser Technol. 139 (2021) 106914, https://doi.org/10.1016/j.optlastec.2021.106914. [ 3] O. Ertuğrul, et al., Effect of HIP process and subsequent heat treatment on microstructure and mechanical properties of direct metal laser sintered AlSi10Mg alloy, Rapid Prototyp. J. 26(8) (2020) 1421 - 1434, https://doi.org/10.1108/RPJ - 07 - 2019 - 0180. [ 4] S. Leuders, et al., On the fatigue properties of metals manufactured by selective laser melting – The role of ductility, J. Mater. Res. 29(17) (2014) 1911 - 1919, https://doi.org/10.1557/jmr.2014.157. [ 5] D. Croccolo, et al., Fatigue response of as - built DMLS maraging steel and effects of aging, machining, and peening treatments, Met. 8(7) (2018) 505, https://doi.org/10.3390/met8070505. [ 6] B. AlMangour, et al., Integration of heat treatment with shot peening of 17 - 4 stainless steel fabricated by direct metal laser sintering, JOM 69(11) (2017) 2309 - 2313, https://doi.org/10.1007/s11837 - 017 - 2538 - 9. [ 7] M. Sugavaneswaran, et al., Enhancement of surface characteristics of direct metal laser sintered stainless steel 316L by shot peening, Surf. Interfaces. 12 (2018) 31 - 40, https://doi.org/10.1016/j.surfin.2018.04.010. [ 8] EOS GmbH, EOS StainlessSteel 316L Material Data Sheet, https://www.eos.info/metal - solutions/metal - materials/data - sheets/mds - eos stainlesssteel - 316l (2025). [ 9] S. Kedziora, et al., Strength properties of 316L and 17 - 4 PH stainless steel produced with additive manufacturing, Matls. 15(18) (2022) 6278, https://doi.org/10.3390/ma15186278.