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The creep and fracture properties of additively manufactured inconel 625

Published

Author(s)

Kwang-Tae Son, Thien Q. Phan, Lyle E. Levine, Kyu-Sik Kim, Kee-Ahn Lee, Magnus Ahlfors, Michael E. Kassner

Abstract

High temperature creep tests of additively manufactured (AM) nickel-based superalloy Inconel 625 (IN 625) and wrought 625 were conducted at 650 ˚C and 800 ˚C over the stress range of 65 MPa to 658 MPa. Thermal treatments were conducted prior to creep testing: either solution heat-treated or hot isostatically pressed and, additionally, long-term cyclic heat-treatments at 650 ˚C (LHT) for 6 months and 1 year. AM 625 showed equal or even higher creep strength than wrought 625 for all heat treatments. However, AM 625 exhibited poor ductility compared to wrought 625 under all creep testing conditions, and the ductility decreased after the LHT. Both AM and wrought 625 obtained some additional strength after the LHT. The amount of extra strength in the alloys was generally proportional to the matrix volume fraction of γ'' phase (650 ˚C) and δ phase (800 ˚C). The creep analysis suggested that dislocation climb is the rate controlling mechanism for creep. Atomic probe tomography revealed that oxygen content at the grain boundaries of creep-deformed AM 625 was too small to cause any embrittlement. Nano-secondary ion mass spectrometer analysis found strong sulfur segregation at Al2O3/matrix interfaces. Fracture is intergranular where Al2O3 (that forms as a result of oxygen absorption by the powder particles before additive manufacturing) is sometimes located. Cracking can occur from these interfaces and repeated sulfur diffusion to the crack tip (analogous to oxygen in 718) was the foremost possibility to explain the poor ductility of AM 625 within the temperature range tested.
Citation
Acta Materialia
Volume
15

Keywords

nickel-based superalloys, laser powder bed fusion, creep, embrittlement, additive manufacturing

Citation

Son, K. , Phan, T. , Levine, L. , Kim, K. , Lee, K. , Ahlfors, M. and Kassner, M. (2021), The creep and fracture properties of additively manufactured inconel 625, Acta Materialia, [online], https://doi.org/10.1016/j.mtla.2021.101021 (Accessed June 15, 2024)

Issues

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Created January 25, 2021, Updated December 10, 2022