PSI - Issue 82

ScienceDirect Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2026) 000–000 Available online at www.sciencedirect.com ScienceDirect Structural Integrity Procedia 00 (2026) 000–000 Available online at www.sciencedirect.com

www.elsevier.com/locate/procedia www.elsevier.com/locate/procedia

Procedia Structural Integrity 82 (2026) 162–168

© 2026 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ICSID organizers Abstract In this work, we explore the feasibility of simplifying the heat treatment of IN939 superalloy prepared by laser-based powder bed fusion to a single step in the process called direct ageing, conducted at 800°C for 8 hours. Tensile tests and strain-controlled low cycle fatigue tests were conducted at room temperature using machined specimens with horizontal and vertical build orientations. Test results were compared with other thermodynamical states of IN939, namely conventional cast, and additively manufactured with and without post heat treatment. Inherent cellular microstructure is further strengthened by γ’ precipitation which enhances tensile strength but reduces ductility. Also, precipitation of carbides and γ/γ’ eutectics at internal interfaces was observed. Low cycle fatigue performance of direct aged samples fares relatively well only in the very high-stress regime. However, the cracking is rather brittle and there is little to none indication of incoming failure. Therefore, skipping the solutioning heat treatment and performing direct ageing of as-built additively manufactured IN939 components is not recommended. © 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ICSID organizers Keywords: Heat treatment optimization, Direct ageing, Low-cycle fatigue, Additive manufacturing, Laser-based powder bed fusion of metals 1. Introduction The cellular microstructure inherent to laser-based powder bed fusion of metals (PBF-LB/M) has proven to break the strength-ductility tradeoff for many materials including IN939 superalloy. Liu (2018) showed that the hierarchical microstructure consisting of dislocation cells which hinder the dislocation movement, resulting in an Abstract In this work, we explore the feasibility of simplifying the heat treatment of IN939 superalloy prepared by laser-based powder bed fusion to a single step in the process called direct ageing, conducted at 800°C for 8 hours. Tensile tests and strain-controlled low cycle fatigue tests were conducted at room temperature using machined specimens with horizontal and vertical build orientations. Test results were compared with other thermodynamical states of IN939, namely conventional cast, and additively manufactured with and without post heat treatment. Inherent cellular microstructure is further strengthened by γ’ precipitation which enhances tensile strength but reduces ductility. Also, precipitation of carbides and γ/γ’ eutectics at internal interfaces was observed. Low cycle fatigue performance of direct aged samples fares relatively well only in the very high-stress regime. However, the cracking is rather brittle and there is little to none indication of incoming failure. Therefore, skipping the solutioning heat treatment and performing direct ageing of as-built additively manufactured IN939 components is not recommended. © 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ICSID organizers Keywords: Heat treatment optimization, Direct ageing, Low-cycle fatigue, Additive manufacturing, Laser-based powder bed fusion of metals 1. Introduction The cellular microstructure inherent to laser-based powder bed fusion of metals (PBF-LB/M) has proven to break the strength-ductility tradeoff for many materials including IN939 superalloy. Liu (2018) showed that the hierarchical microstructure consisting of dislocation cells which hinder the dislocation movement, resulting in an 8th International Conference on Structural Integrity and Durability (ICSID2025) Low-cycle fatigue of direct aged PBF-LB/M IN939 superalloy Tomáš Babinský a,b, *, Ladislav Poczklán b , Jakub Poloprudský b , Libor Trško c , Ivo Šulák b 8th International Conference on Structural Integrity and Durability (ICSID2025) Low-cycle fatigue of direct aged PBF-LB/M IN939 superalloy Tomáš Babinský a,b, *, Ladislav Poczklán b , Jakub Poloprudský b , Libor Trško c , Ivo Šulák b a Center for Nuclear Engineering and Sciences, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland b Institute of Physics of Materials, Czech Academy of Sciences, Žižkova 513/22, 61600 Brno, Czech Republic c Research Centre UNIZA, University of Žilina, Univerzitná 8215/1, 01026 Žilina, Slovak Republic a Center for Nuclear Engineering and Sciences, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland b Institute of Physics of Materials, Czech Academy of Sciences, Žižkova 513/22, 61600 Brno, Czech Republic c Research Centre UNIZA, University of Žilina, Univerzitná 8215/1, 01026 Žilina, Slovak Republic

* Corresponding author. Tel.: +41 56 310 27 52 E-mail address: tomas.babinsky@psi.ch * Corresponding author. Tel.: +41 56 310 27 52 E-mail address: tomas.babinsky@psi.ch

2452-3216 © 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ICSID organizers 2452-3216 © 2026 The Authors. Copy from the contract: Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ICSID organizers

2452-3216 © 2026 The Authors. Published by ELSEVIER B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of ICSID organizers 10.1016/j.prostr.2026.04.025