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The effect of heat treatments on the elevated temperature mechanical performance of directed energy deposition repaired Ni-based superalloys
Journal of Materials Research and Technology, Volume: 43, Pages: 60 - 78
Swansea University Authors:
Kieran Samuel, Nick Barnard, Robert Lancaster
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© 2026 The Authors. This is an open access article distributed under the terms of the Creative Commons CC-BY license.
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DOI (Published version): 10.1016/j.jmrt.2026.06.061
Abstract
Laser-blown powder directed energy deposition (LBP-DED) is being explored for repairing forged Ni-based superalloy components. However, the high cooling rates associated with these processes develop an as-deposited microstructure that is distinct from that of the forged substrate. As such, elemental...
| Published in: | Journal of Materials Research and Technology |
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| ISSN: | 2238-7854 2214-0697 |
| Published: |
Elsevier BV
2026
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| Online Access: |
Check full text
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| URI: | https://cronfa.swan.ac.uk/Record/cronfa72020 |
| Abstract: |
Laser-blown powder directed energy deposition (LBP-DED) is being explored for repairing forged Ni-based superalloy components. However, the high cooling rates associated with these processes develop an as-deposited microstructure that is distinct from that of the forged substrate. As such, elemental segregation, brittle interdendritic phases, and local mechanical mismatches can occur within these deposits. The current knowledge gap relates to how repair-compatible ageing heat treatments impact Alloy 718Plus deposits made on both forged Alloy 718 and forged Alloy 718Plus substrates, and if they can be utilised to enhance metallurgical compatibility while avoiding homogenisation heat treatments. For this reason, both forged substrates were repaired using Alloy 718Plus powder by LBP-DED and exposed to either Alloy 718 or Alloy 718Plus compatible ageing heat treatments. Microscopy, compositional analysis, electron backscatter diffraction, Vickers microhardness, tensile testing at 650 °C, and fractographic analyses were used to characterise the repairs. Both heat treatment conditions displayed distinct substrate, bond-line, heat affected, and LBP-DED repair zones. The repair deposit exhibited columnar dendritic grains with chain-like and granular interdendritic Laves phase remaining, indicating that the inherited as-deposited microstructure dominates the final microstructure. Heat treatment resulted in the precipitation of γ′, as well as the local formation of η phase near Laves phase regions, yet did not significantly alter grain size or dendrite arm spacing. Additionally, the prior forged microstructure controlled epitaxial grain growth behaviours with larger forged Alloy 718 grains promoting larger LBP-DED grains. The 718-718Plus condition exhibited improved ductility at 650 °C compared to the 718Plus-718Plus condition. Fractographic analysis confirmed that failure occurred within the LBP-DED repair zone and was attributed primarily to strain incompatibility between the brittle Laves phase and the γ matrix. In summary, ageing heat treatment resulted in limited changes to the as-deposited Alloy 718Plus microstructure, whereas the substrate and as-deposited microstructures had more pronounced effects on the final metallurgical and mechanical behaviour. |
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| Keywords: |
Alloy 718; Alloy 718Plus; Laser-blown powder directed energy deposition (LBP-DED); Heat treatments; Mechanical properties |
| College: |
Faculty of Science and Engineering |
| Funders: |
The current research was funded under the EPSRC Industrial Case Award EP/W524694/1. The provisions of research bursary, materials, and supporting information from Rolls-Royce plc. Is gratefully acknowledged. Mechanical tests were performed at SMaRT. Utilisation of the FEG-SEM was provided by Swansea University's Advanced Imaging of Materials (AIM) Facility, which was funded by the EPSRC (EP/M028267/1), The European Regional Development Fund through the Welsh Government (80708) and the Ser Solar project via the Welsh Government. |
| Start Page: |
60 |
| End Page: |
78 |