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Open AccessFeature PaperArticle

Aging of γ′ Precipitates at 750 °C in the Nickel-Based Superalloy AD730TM: A Thermally or Thermo-Mechanically Controlled Process?

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Pprime Institute, UPR CNRS 3346 CNRS-ENSMA, University of Poitiers, ISAE-ENSMA – Teleéport 2, 1st Clément Ader Avenue, BP 40109, 86961 Futuroscope Chasseneuil CEDEX, France
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SAFRAN TECH, Jeunes Bois Street, Châteaufort, CS 80112, 78772 Magny les Hameaux, France
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Authors to whom correspondence should be addressed.
Metals 2020, 10(4), 426; https://doi.org/10.3390/met10040426 (registering DOI)
Received: 17 February 2020 / Revised: 23 March 2020 / Accepted: 24 March 2020 / Published: 25 March 2020
(This article belongs to the Special Issue Advances in Superalloys and High Temperature Intermetallics)
The microstructural stability during aging at 750 °C of the γ/γ′ nickel-based superalloy AD730TM is investigated in this work. Strain-free aging and aging during fatigue tests are conducted, with a focus on the influence of the strain ratio, the maximum applied strain, and the cycle waveform (with or without dwell). Two classical mechanisms of γ′ precipitates aging are identified at 750 °C: the coarsening of small spherical γ′ precipitates via the thermally-activated Ostwald ripening process and the coalescence of at least two precipitates into one. These mechanisms appeared to be concomitant during aging. It has been demonstrated that the coarsening kinetics of γ′ precipitates can be described by a classical Lifshitz-Slyozow-Wagner (LSW) equation. The introduction of a cyclic strain during aging at 750 °C increases the coarsening kinetics by means of changes in the volume diffusion of γ′-forming elements and of constraint misfit effects. More precisely, it is shown that the higher the maximum applied strain and/or the strain rate, the higher the coarsening rates. Finally, dwell-fatigue promotes the activation of the γ′ coalescence at 750 °C. View Full-Text
Keywords: nickel-based superalloys; growth mechanisms; coarsening; coalescence; fatigue; creep-fatigue; γ′ precipitates; high temperature nickel-based superalloys; growth mechanisms; coarsening; coalescence; fatigue; creep-fatigue; γ′ precipitates; high temperature
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Mrozowski, N.; Hénaff, G.; Hamon, F.; Rouffié, A.-L.; Franchet, J.-M.; Cormier, J.; Villechaise, P. Aging of γ′ Precipitates at 750 °C in the Nickel-Based Superalloy AD730TM: A Thermally or Thermo-Mechanically Controlled Process? Metals 2020, 10, 426.

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