Multi-Scale Characterization of Different Generations of Gamma Prime Precipitates in Nickel-based Superalloys Using Correlative Microscopy Techniques

Nickel-based superalloys have been widely used for elevated temperature applications such as turbine disc of jet engines due to their excellent mechanical properties. The typical microstructure of these alloys primarily consists of dispersed precipitates of the ordered γ’ phase with L12 structure within a disordered face-centered cubic γ matrix. The γ -γ’ microstructure in these alloys can be controlled via a combination of composition and cooling rate from the high temperature single γ phase field during processing. Typically during continuous cooling from γ’supersolvus temperature, various size scales of γ’ precipitates are formed, primarily due to multiple nucleation events occurring at various temperatures in the γ -γ’ regime [1,2]. The complex interplay between thermodynamic and kinetic factors lead to the formation of a complex microstructure consisting of a multimodal size distribution of γ’ precipitates (often consisting of three different distinct size distributions ranging from microns to nanometers) and γ’ precipitate-free zones, within the γ matrix. The precipitates not only differ in their size and morphology but also in nucleation density and compositions. The resulting morphology, volume fraction, size distribution of these γ’ precipitates determine the mechanical properties of these alloys [3,4].