Eta Phase Precipitation at Equilibrium and in Strain Free ATI 718Plus

Abstract:

As aerospace engines advance to obtain higher thermal efficiencies, it is imperative to develop high temperature materials. Inconel 718 is a nickel-based superalloy that has been used for decades in aero-engine parts as it allows for use in high temperature applications. ATI 718Plus is a newer nickel-based superalloy that has been developed with a 55°C higher temperature capability over Inconel 718. ATI 718Plus components are manufactured by forging a wrought billet in stages to obtain the desired geometry and microstructure. Parts are heat treated to optimised proportions of γ’ and η phases. η phase is an acicular phase that precipitates on the grain boundaries, whereas γ’ is the primary strengthening phase. η phase is an important phase to understand as it is utilised in controlling the grain size during hot working processes at temperatures below its solvus temperature. When η phase is fully solutioned, the grain size is free to increase and hence the material mechanical properties can become detrimental. The short-term precipitation kinetics of η phase in strain-free ATI 718Plus is still not completely understood. In this study, the aims and objectives were to study the η precipitation kinetics in strain-free material as well as studying η phase precipitation in equilibrium conditions. TTT diagrams were produced for the η phase in strain-free material and compared to the limited data available in the open literature. In addition, the equilibrium η phase content, aspect ratio, length and width were determined and compared to the very little data that is currently published.

• Periodical: Solid State Phenomena (Volume 353)
• Pages: 79-84
• DOI: https://doi.org/10.4028/p-F9HnsO
• Online since: December 2023
• Authors: Bilal Hassan*, Yann Jansen, Sebastien Nouveau, Jonathan Corney
• Keywords: ATI 718Plus, Equilibrium, Eta Phase, Precipitation Kinetics, η Phase

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