PSI - Issue 66

Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2025) 000–000 Available online at www.sciencedirect.com ScienceDirect

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Procedia Structural Integrity 66 (2024) 256–264

8th International Conference on Crack Paths Corrosion Fatigue Mechanisms of Diffusion Brazed Metastable Austenite Joints with Nickel-Based Filler Metal Johannes L. Otto a, *, Cedric Marroni a , Fabian Bersch a , Lukas M. Sauer a , Hanigah Kanagarajah a , Frank Walther a a TU Dortmund University, Chair of Materials Test Engineering (WPT), Baroper Str. 303, 44227 Dortmund, Germany Abstract Diffusion brazing with nickel-based filler metals is frequently used for joining steels when components are subjected to high static or dynamic loads, corrosive environments and elevated temperatures. Due to the necessary melting point depressing metalloids of the filler metals, such as boron and silicon, brittle precipitations are formed during the brazing process depending on the diffusion mechanisms. These brittle borides and silicides can significantly affect the crack initiation and propagation as well as the overall lifetime of the joints, since the corrosion and fatigue mechanisms change depending on the chemistry, quantity, size, location and morphology of the precipitations. To investigate these mechanisms for an isothermal solidified brazing seam the metastable austenite AISI 304L was used to braze cylindrical butt joints at 1160°C under vacuum atmosphere with an experimental filler metal based on the NiCrSiB system with additions of Fe and Mo. Specimens were then fatigued with different stress amplitudes at tension-tension ratio in air atmosphere and inside a new self-developed corrosion chamber with different aqueous corrosive atmospheres at different temperatures with and without the presence of chloride ions to generate characteristic SN-curves. It was shown that chromium-rich borides in the diffusion zone begin to break up, particularly at high stress amplitudes when cyclic creep occurred, promoting local corrosion mechanism and thus dominating crack initiation and propagation. However, stress corrosion cracking was observed at an elevated temperature of 80 °C in corrosive atmospheres containing chloride ions. As a result, multiple additional cracks occurred outside the brazing seam, reducing the fatigue life significantly. © 2025 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 CP 2024 Organizers Keywords: TLP-Bonding; AISI 304L; NiCrSiB; Microstructure; Creep fatigue; Cracks Paths; Stress Corrosion Cracking © 2025 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 CP 2024 Organizers

* Corresponding author. Tel.: +49 231 755 8536; fax: +49 231 755 8029. E-mail address: Johannes.otto@tu-dortmund.de

2452-3216 © 2025 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 CP 2024 Organizers

2452-3216 © 2025 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 CP 2024 Organizers 10.1016/j.prostr.2024.11.108