Gamma Prime Precipitate Evolution During Aging of a Model Nickel-Based Superalloy

A J Goodfellow,T Martin,C D Boyer,K A Christofidou,M C Hardy,N G Jones,E I Galindo-Nava,H J Stone,P A J Bagot

doi:10.1007/s11661-017-4336-y

A J Goodfellow, T Martin + Show 7 more

Open Access

https://doi.org/10.1007/s11661-017-4336-y

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Abstract

The microstructural stability of nickel-based superalloys is critical for maintaining alloy performance during service in gas turbine engines. In this study, the precipitate evolution in a model polycrystalline Ni-based superalloy during aging to 1000 hours has been studied via transmission electron microscopy, atom probe tomography, and neutron diffraction. Variations in phase composition and precipitate morphology, size, and volume fraction were observed during aging, while the constrained lattice misfit remained constant at approximately zero. The experimental composition of the γ matrix phase was consistent with thermodynamic equilibrium predictions, while significant differences were identified between the experimental and predicted results from the γ′ phase. These results have implications for the evolution of mechanical properties in service and their prediction using modeling methods.

Highlights

POLYCRYSTALLINE Ni-based superalloys are the material of choice for many high-temperature structural applications in gas turbine engines
Microstructural analysis revealed that the size of the secondary γ′ precipitates remained approximately constant during the early stages of aging, but exhibited the morphological instabilities associated with precipitate splitting following longer duration exposures
When the tertiary γ′ precipitates were present in the microstructure, they were observed to coarsen in line with LSW theory

Summary

Introduction

POLYCRYSTALLINE Ni-based superalloys are the material of choice for many high-temperature structural applications in gas turbine engines. Their remarkable mechanical performance is derived from the presence of an ordered L12 (strukturbericht notation) γ′ precipitate phase within the disordered A1 γ matrix. The precipitate size at which peak strength is obtained corresponds to the transition from weak to strong pair dislocation coupling and, as such, varies with alloy composition.

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