PSI - Issue 82

Tomáš Babinský et al. / Procedia Structural Integrity 82 (2026) 162–168 Tomáš Babinský et al. / Structural Integrity Procedia 00 (2026) 000–000

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5. Conclusions Following the microstructural scrutiny, fatigue testing and post-test fractography, direct ageing at 800 °C/8 h does not seem to be a viable heat treatment for PBF-LB/M IN939. Direct ageing successfully introduces strengthening γ’ precipitates while preserving the hierarchical cellular microstructure but also promotes carbide precipitation and precipitation of embrittling γ/γ eutectics at internal interfaces, particularly grain boundaries. The extraordinary strength comes at the cost of reduced ductility and rather brittle cracking behavior with little or no indication of incoming failure. This becomes evident particularly at relatively low-stress fatigue (towards the high cycle regime) when the cumulative plastic strains are high and resistance to cyclic plastic straining largely determines the resulting fatigue life. Furthermore, the presence of the γ/γ’ eutectics suggests mediocre high temperature mechanical properties. Therefore, wider industrial use of direct ageing is unlikely. Acknowledgements The present research was financially supported by the grant No. 23-06167S of the Czech Science Foundation (GACR), and the project "Mechanical Engineering of Biological and Bio-inspired Systems", funded as project No. CZ.02.01.01/00/22_008/0004634 by Programme Johannes Amos Commenius, call Excellent Research of the Ministry of Education, Youth and Sports of the Czech Republic. Ivo Šulák appreciates the support of the Czech Academy of Sciences under the framework of the Lumina quaerentur project. Data availability Babinský, T., Šulák, I., Gálíková, M., Kuběna, 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. Bean, C., Wang, F., Charpagne, M.A., Villechaise, P., Valle, V., Agnew, S.R., Gianola, D.S., Pollock, T.M., Stinville, J.C., 2022. Heterogeneous slip localization in an additively manufactured 316L stainless steel. International Journal of Plasticity 159, 103436. Delargy, K.M., Shaw, S.W.K., Smith, G.D.W., 1986. Effects of heat treatment on mechanical properties of high-chromium nickel-base superalloy IN 939. Materials Science and Technology 2, 1031–1037. Dogu, M.N., Ozer, S., Yalcin, M.A., Davut, K., Bilgin, G.M., Obeidi, M.A., Brodin, H., Gu, H., Brabazan, D., 2023. Effect of solution heat treatment on the microstructure and crystallographic texture of IN939 fabricated by powder bed fusion-laser beam. Journal of Materials Research and Technology 24, 8909–8923. ISO 12106:2017. Metallic materials – Fatigue testing – Axial-strain-controlled method. Mar. 2017 ISO 6892-1:2019. Metallic materials – Tensile testing – Part 1: Method of test at room temperature. Nov. 2019. 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. Kumar, C., Reddy, S., Eswaramoorthy, N.K., Ravanappa, P., Chintapenta, V., Srinivasan, D., Kumar, P., 2024. Microstructure optimization for improving creep resistance of additively manufactured Ni-based superalloy IN939 through heat treatment. Journal of Materials Science 60, 1545–1560. Li, J., Shrestha, S.L., Long, Y., Zhijun, L., Xintai, Z., 2016. The formation of eutectic phases and hot cracks in one Ni-Mo-Cr superalloy. Materials and Design 93, 324–333. Liu, L., Ding, Q., Zhong. Y., Zou, J., Wu, J., Chiu, Y.L., Li, J., Zhang, Z., Yu, Q., Shen, Z., 2018. Dislocation network in additive manufactured steel breaks strength-ductility trade-off. Materials Today 21, 354–361. Pham, M.S., Dovgyy, B., Hooper, P.A., Gourlay, C.M., Piglione, A., 2020. The role of side-branching in microstructure development in laser powder-bed fusion. Nature Communications 11, 749. Šulák, I., Babinský, T., Chlupová, A., Milovanović, A., Náhlík, L., 2023. Effect of building direction and heat treatment on mechanical properties of Inconel 939 prepared by additive manufacturing. Journal of Mechanical Science and Technology 37, 1071–1076. Tang, Y.T., Panwisawas, C., Ghoussoub, J.N., Gong, Y., Clark, J.W.G., Németh, A.A.N., McCartney, D.G., Reed, R.C., 2021. Alloys-by-design: application to new superalloys for additive manufacturing. Acta Materialia 202, 417–436. Wan, H.Y., Zhou, Z.J., Li, C.P., Chen, G.F., Zhang, G.P., 2018. Effect of scanning strategy on grain structure and crystallographic texture of Inconel 718 processed by selective laser melting. Journal of Materials Science and Technology 34, 1799–1804. Data have been shared online in Zenodo repository, DOI: 10.5281/zenodo.17493779. References