Vogel, F.; Ngai, S.; Fricke, K.; McKechnie, M.; Wanderka, N.; Hentrich, T.; Banhart, J.; Thompson, G.B.: Tracing the three-dimensional nanochemistry of phase separation in an inverse Ni-based superalloy. Acta Materialia 157 (2018), p. 326-338
10.1016/j.actamat.2018.07.038

Abstract:
Tailoring the properties of intermetallic alloys and phases, which resemble the foundation of a vast variety of high-temperature materials like nickel-based superalloys, is a challenge for improving this class of materials that requires comprehensive understanding of their three-dimensional (3D) nanochemistry. Here we use high-resolution microscopy techniques to reveal the microstructural and 3D nanochemical evolution of disordered γ particles from nanoscale nickel-rich heterogeneities (clusters) to γ spheres and then γ plates in an inverse Ni78Al13Ti9 alloy having an ordered (L12) γ′ matrix. The γ particles require aging to achieve a thermodynamically stable morphology and composition, determined by reducing the Gibbs free energy. The fundamental analogy between γ particles in a γ′ matrix of an inverse alloy and γ particles in γ′ precipitates of a hierarchical Ni86.1Al8.5Ti5.4 alloy is established. Our results demonstrate that this analogy can be harnessed as a novel approach for improving the properties of nickel-based superalloys.