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

Abstract

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.

Evaluation of high-frequency induction heat sintering and conventional sintering in AlxCoCrFeMnNi high-entropy alloys

“…In addition, there are generally two main mechanisms to decrease the surface energy of the system: coarsening and coalescence. In this regard, coarsening occurs when the interfacial energy is reduced through a mass transfer process by diffusion from high interfacial energy precipitates to low interfacial energy precipitates, significantly altering their morphology [53][54][55][56]. This energy minimization leads to the growth of larger particles at the expense of smaller particles.…”

“…On the other hand, the union between two precipitates due to the overlap of their interdifusional zones (coalescence) is also observed (Fig 4 b.) [53][54][55][56].…”

High-performance IN738 superalloy derived from turbine blade waste for efficient electrooxidation of ethanol, ethylene glycol, and urea

“…Two-phase microstructure like gamma (γ) and gamma-prime (γ') is mainly responsible for the high-temperature strength and high creep deformation resistance. [37] Please Insert Fig. 1 3…”

High-performance IN738 superalloy derived from turbine blade waste for efficient ethanol, ethylene glycol, and urea electrooxidation

“…[36] However, aluminum and titanium are considered essential solutes in nickel-based superalloys. Two-phase microstructure like gamma (γ) and gamma-prime (γ') is mainly responsible for the high-temperature strength and high creep deformation resistance [37].…”