Observation of the Dissolution of Topologically Close Packed Phases by an Additional Heat Treatment in Third Generation Nickel‐Based Single Crystal Superalloy Turbine Blades

Topologically close packed (TCP) phases degrade the superior creep and rupture properties of Ni‐based single crystal superalloys. Initially, small TCP phases are formed in the dendrite core during the early stages of the manufacturing process, such as solution heat treatment, and surrounded by a gamma prime (γ′) phase. Then, TCP phases continue to develop during full heat treatment. However, an additional heat treatment induces diffusion of refractory metals from the TCP phases into the γ′ phase and consequently, the TCP phases clearly disappear. After dissolution, the regions where the TCP phases existed are altered to a normal microstructure composed of γ channels and a normal cubic γ′ phase. Based on the observation result, the mechanism of the dissolution of TCP phases is discussed.