Mapping the evolution of hierarchical microstructures in a Ni-based superalloy

Area of Science:

• Materials Science
• Metallurgy
• Physical Chemistry

Background:

• Phase separation of gamma-prime (γ′) precipitates is crucial for nickel-based superalloys' microstructure and mechanical properties.
• During aging, disordered gamma (γ) spheres form within ordered γ′ precipitates, transforming into plates and eventually splitting the γ′ precipitates.
• The presence of γ particles within γ′ impacts coarsening kinetics and enhances alloy hardness.

Purpose of the Study:

• To visualize and quantify the phase separation process in a specific nickel-based superalloy (Ni86.1Al8.5Ti5.4) using atom probe tomography.
• To understand the compositional evolution of γ particles during their morphological transformation.
• To investigate the role of nickel supersaturation in driving γ particle formation and subsequent phase separation.

Main Methods:

• Atom probe tomography (APT) was employed for three-dimensional visualization of phase separation.
• APT provided near-atomic resolution compositional analysis of all phases present.
• The study focused on a Ni86.1Al8.5Ti5.4 alloy during its aging process.

Main Results:

• Phase separation was observed within γ′ precipitates, characterized by the formation and evolution of γ particles.
• γ′ precipitates were found to be supersaturated in nickel, which drives the formation of γ particles.
• A clear compositional evolution of γ particles was observed, correlating with their morphological changes from spheres to plates.

Conclusions:

• Nickel supersaturation within γ′ precipitates is a key factor controlling the phase separation process.
• The observed phase separation and compositional evolution of γ particles directly influence the microstructure of nickel-based superalloys.
• Tailoring nickel supersaturation offers a pathway to control phase separation and optimize the mechanical properties of these advanced alloys.