PSI - Issue 80

Marie Kvapilová et al. / Procedia Structural Integrity 80 (2026) 269–278 Author name / Structural Integrity Procedia 00 (2019) 000–000

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5. Conclusion • The creep behaviour of IN939 produced by L-PBF corresponds to the power-law creep regime, with stress exponents indicating dislocation climb controlled by diffusion as the dominant deformation and fracture mechanism. • The absence of a distinct secondary creep stage and the presence of only an inflection point in strain-rate curves suggest limited recovery and metastable microstructure under stress. • Similar values of the stress exponents n and m across conditions suggest that the same microstructural mechanism governs both creep deformation and fracture. • Grain boundary effects, such as carbide coarsening or grain boundary sliding, may contribute to deformation mechanisms at lower applied stresses. • The microstructural evolution after creep exposure is highly dependent on stress and temperature: lower stresses lead to grain elongation and microcracking near grain boundaries, while higher stresses cause more widespread damage, including cracking further from the fracture surface. • Prolonged high-temperature exposure results in grain growth and coarsening of MC-type carbides and γ ′ precipitates, with significant changes observed especially at 900 °C, where γ particles grow, lose their spheroidal shape, and show signs of coalescence. • Fractographic analysis showed that fracture morphology evolves with temperature and stress; while lower temperatures preserve the original grain-boundary-aligned fracture typical of L-PBF materials, higher temperatures and prolonged exposure promote grain growth and carbide coarsening, leading to fracture along thermally modified grain boundaries and increased specimen ductility. Acknowledgements The present study was financially supported by the grant No. 23-06167S of the Czech Science Foundation (GACR). References Babinský, T., Šulák, I., Gálíková, M., Kubĕna, I., Poloprudský, J., & Náhlík, L. (2025). Room-temperature low-cycle fatigue behaviour of cast and additively manufactured IN939 superalloy. Materials Science and Engineering: A, 924, 147730. https://doi.org/10.1016/j.msea.2024.147730 Banoth, S., Li, C.-W., Hiratsuka, Y., & Kakehi, K. (2020). The Effect of Recrystallization on Creep Properties of Alloy IN939 Fabricated by Selective Laser Melting Process. Metals, 10(8), Article 8. https://doi.org/10.3390/met10081016 Čadek, J. (1988). Creep in Metallic Materials. Elsevier. https://books.google.cz/books?id=8WlmnQAACAAJ Gibbons, T. B., & Stickler, R. (1982). IN939: Metallurgy, Properties and Performance. In R. Brunetaud, D. Coutsouradis, T. B. Gibbons, Y. Lindblom, D. B. Meadowcroft, & R. Stickler (Ed.), High Temperature Alloys for Gas Turbines 1982 (s. 369–393). Springer Netherlands. https://doi.org/10.1007/978-94-009-7907-9_15 Jahangiri, M. R., Arabi, H., & Boutorabi, S. M. A. (2014). Comparison of microstructural stability of IN939 superalloy with two different manufacturing routes during long-time aging. Transactions of Nonferrous Metals Society of China, 24(6), 1717–1729. https://doi.org/10.1016/S1003-6326(14)63245-3 Kanagarajah, P., Brenne, F., Niendorf, T., & Maier, H. J. (2013). Inconel 939 processed by selective laser melting: Effect of microstructure and temperature on the mechanical properties under static and cyclic loading. Materials Science and Engineering: A, 588, 188–195. https://doi.org/10.1016/j.msea.2013.09.025 Kassner, M. E. (2004). Taylor hardening in five-power-law creep of metals and Class M alloys. Acta Materialia, 52(1), 1–9. https://doi.org/10.1016/j.actamat.2003.08.019 Kassner, M. E. (2009). Fundamentals of creep in metals and alloys (2nd ed). Elsevier. Kulkarni, A. (2018). Additive Manufacturing of Nickel Based Superalloy. arXiv: Applied Physics. https://www.academia.edu/68986390/Additive_Manufacturing_of_Nickel_Based_Superalloy Kvapilova, M., Dvorak, J., Kral, P., Hrbacek, K., & Sklenicka, V. (2019). Creep behaviour and life assessment of a cast nickel – base superalloy MAR – M247. High Temperature Materials and Processes, 38(2019), 590–600. https://doi.org/10.1515/htmp-2019-0006 Kvapilova, M., Kral, P., Dvorak, J., & Sklenicka, V. (2021). High Temperature Creep Behaviour of Cast Nickel-Based Superalloys INC 713 LC, B1914 and MAR-M247. Metals, 11(1), Article 1. https://doi.org/10.3390/met11010152 Marchese, G., Parizia, S., Saboori, A., Manfredi, D., Lombardi, M., Fino, P., Ugues, D., & Biamino, S. (2020). The Influence of the Process Parameters on the Densification and Microstructure Development of Laser Powder Bed Fused Inconel 939. METALS, 10(7), 882. https://doi.org/10.3390/met10070882