On the Dissolution of the γ′ Phase at the Dendritic Scale in a Rhenium-Containing Nickel-Based Single Crystal Superalloy After High Temperature Exposure

MCNG is a nickel base single crystal superalloy containing both rhenium and ruthenium. The γ′ phase dissolution evolutions have been studied after very high temperature exposures for various times up to the thermodynamic equilibrium. Very different γ′ phase dissolution behaviors have been observed across the dendritic structure. In the temperature range investigated, the dissolution of the γ′ phase is more pronounced within the dendrites compared to its dissolution observed within the interdendrites. The physical parameters likely to promote the different dissolution behavior at the dendritic scale such as the diffusion coefficients of the major alloying elements, the γ′ solvus temperature, and the γ′ precipitates morphologies are discussed. Special attention is paid to the very first steps of the dissolution process.