PSI - Issue 77

Karel Trojan et al. / Procedia Structural Integrity 77 (2026) 537–542 Karel Trojan / Structural Integrity Procedia 00 (2026) 000–000

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First, the macroscopic residual stresses along the axial direction in the surface layers, which is critical under tensile loading, are approximately 500 MPa lower in SP120. Since residual stresses combine with applied stresses during fatigue testing, lower tensile residual stress delays the crack initiation. Second, SP120 also shows higher full width at half maximum (FWHM) values for its diffraction peaks. This indicates either smaller crystallite sizes and/or increased microstrain. Elevated microstrain is typically associated with a higher dislocation density, while smaller crystallites often correlate with reduced grain size . According to the Hall Petch relationship, which follows the inverse square root dependence of ( −1 / 2 ), the fatigue limit tends to increase as grain size decreases. This effect has been confirmed for maraging steels by Rohit et al. (2021), who demonstrated that grain boundaries act as barriers to fatigue crack propagation. Thus, increased dislocation density and finer grains contribute to reduced dislocation mobility and slower fatigue crack initiation and growth. Additionally, the untreated surface of additively manufactured samples tends to exhibit higher roughness, which negatively impacts fatigue life, as shown by Petan et al. (2019). However, their research also highlighted that the presence of favourable surface residual stresses, particularly compressive stresses introduced via laser shock peening, can significantly enhance fatigue performance. Our future research will focus on further optimization of both surface characteristics and, more importantly, the residual stress state, aiming to improve fatigue resistance in additively manufactured components. 4. Conclusions The study showed that increasing the build platform temperature during printing significantly reduces tensile residual stresses in the surface layers and alters the microstructure, resulting in smaller crystallites and/or higher microstrain. These changes positively affect fatigue performance, as samples printed at higher temperatures exhibited longer fatigue life and a higher endurance limit. To accurately assess the residual stress state in additively manufactured components, it is essential to analyse not only the surface but also the depth profile using X-ray diffraction. Surface measurements alone can overlook significant variations in stress and microstructural parameters beneath the surface, which critically influence fatigue behaviour and mechanical performance. Depth-resolved analysis provides a more complete understanding of stress distribution in the subsurface layers and its impact on crack initiation and propagation. Acknowledgements This publication was prepared as part of a project that was co-financed from the state budget by the Technology agency of the Czech Republic under the Sigma Programme, project “Applied Research on Process Parameters of 3D Printing Tool Steel to Minimize Residual Stresses”, No. TQ03000457, see https://tacr.gov.cz/en/. References Bartlett, J. L. and Li, X., 2019. An overview of residual stresses in metal powder bed fusion. Additive Manufacturing, 27, 131–149. Bhadeshia, H.K.D.H., 2002. Effect of materials and processing: Material factors, in “Handbook of Residual Stress and Deformation of Steel ”. Totten, G., Howes, M., Inoue, T. (Eds.). ASM International: Materials Park, OH, USA, 3–10. Černý , I., Čapek , J., Kec, J., Trojan, K., Ganev, N., Němeček , S., 2023. Fatigue of Laser-Welded Structures: Role of Residual Stress, in “Comprehensive Structural Integrity ”. Aliabadi F. and Soboyejo W. (Eds.). Elsevier Science, ISBN 9780128229446. Köhler, H., Partes K., Kornmeier J.R., Vollertsen, F., 2012. Residual stresses in steel specimens induced by laser cladding and their effect on fatigue strength. Phys. Procedia 2012, 39, 354–361. Murray, C.E., Noyan, I.C., 2013. Applied and residual stress determination using X-ray diffraction, in: “Practical Residual Stress Measurement Methods ”. Schajer, G.S. (Ed.); John Wiley & Sons: Chichester, UK, 139–161. Petan, L., Grum, J., Porro, J.A., Luis Ocana, J., R. Sturm, 2019, Fatigue Properties of Maraging Steel after Laser Peening, Metals, 9(12), 1271. Rohit, B., and Nageswara R. M., 2021. Fatigue behavior of 18% Ni maraging steels: a review. Journal of Materials Engineering and Performance 30.4, 2341–12354. Schneller W., Leitner M., Pomberger S., Springer S., Beter F. and Grün F., 2019. Effect of post treatment on the microstructure, surface roughness and residual stress regarding the fatigue strength of selectively laser melted AlSi10Mg structures, Journal of Manufacturing and Materials Processing, 3(4), 89.