On the thermomechanical aging of LPBF alloy 718

Sanchez, Salomé; Gaspard, G.; Hyde, C. J.; Ashcroft, I. A.; Ravi, G. A.; Clare, A. T.

Abstract

Heat treatment of products post additive manufacture are considered hugely important since the metallurgical condition post process is suboptimal. In the case of nickel-based superalloys, grain size, precipitate distribution and precipitate size are distinct from wrought equivalents. Appropriate heat treatment is required to ensure material performance. In this study, LPBF alloy 718, post-processed using a standard heat treatment, is explored under thermal and thermomechanical exposure conditions (with and without applied stress) to illustrate textural and microstructural evolution. The results show the instability of the LPBF microstructure in terms of grain size, precipitate density, and crystallographic orientation, illustrating the need for an appropriate heat treatment in relation to future service conditions. During thermal exposure only, the instability of the LPBF alloy microstructure was evident as the texture increased with time before decreasing and almost disappearing at the time of fracture. This contrasts with wrought alloy whose texture increases throughout creep testing and reaches a maximum at the time of fracture. An ideal microstructure for improved creep performance was identified and includes large equiaxed grains, elimination of texture, dissolution of Laves and δ phase and the precipitation of small carbides and γ’’ precipitates. Recommendations on how to heat treat LPBF alloy 718 to reach this microstructure are given. Overall, this work showed that LPBF components may become more performant than wrought and conventional equivalents.

Citation

Sanchez, S., Gaspard, G., Hyde, C. J., Ashcroft, I. A., Ravi, G. A., & Clare, A. T. (2022). On the thermomechanical aging of LPBF alloy 718. Materials Science and Engineering: A, 841, Article 142998. https://doi.org/10.1016/j.msea.2022.142998

• Journal Article Type: Article
• Acceptance Date: Mar 14, 2022
• Online Publication Date: Mar 29, 2022
• Publication Date: Apr 28, 2022
• Deposit Date: Apr 7, 2022
• Publicly Available Date: Apr 8, 2022
• Journal: Materials Science and Engineering A
• Print ISSN: 0921-5093
• Electronic ISSN: 0921-5093
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 841
• Article Number: 142998
• DOI: https://doi.org/10.1016/j.msea.2022.142998
• Keywords: Mechanical Engineering; Mechanics of Materials; Condensed Matter Physics; General Materials Science
• Public URL: https://nottingham-repository.worktribe.com/output/7712712
• Publisher URL: https://www.sciencedirect.com/science/article/pii/S0921509322004051?via%3Dihub