Microstructural Investigation of the Formation and Development of Topologically Close-Packed Phases in a 3rd Generation Nickel-Base Single Crystal Superalloy

Topologically close-packed (TCP) phases generally form during long period aging or in-service. In this study, however, the early stage formation and development of TCP phases, which has received relatively less attention, was extensively investigated from as-cast samples through to fully heat-treated ones. TCP phases were surrounded with a phase, and their compositions were slightly different due to the structural and compositional complexity. Most of all, extremely fine particles of about 100nm containing large amounts of rhenium formed in the early processing. In addition, two different types of particles were detected at different formation stages: round-shaped particles at the starting point, and needle-like ones near the terminating point. Based on experimental observations, it was suggested that the needle-like particle probably showed the growth of a TCP phase by the diffusion of rhenium after nucleation from a point containing high amounts of rhenium.