Detection of an Intermediate Layer Containing a Rhenium-Rich Particle at Grain Boundaries Formed Within Single Crystal Nickel-Based Superalloys

A stray grain exposed on the surface of a Re-containing single crystal Ni-based superalloy turbine blade was examined by high-resolution analytic electron microscopy. An intermediate layer with the size range of 3 to 4 μm, composed of elongated γ′ phase, was clearly detected forming a boundary between a normal matrix grain and a stray grain. Beyond the intermediate layer, the {100} direction of the γ′ phase in the matrix changed slightly, and a stray grain was formed. In each γ′ grain in the intermediate boundary, a Re-rich region of the size range of 100 to 200 nm was detected, suggesting a role for rhenium in the formation of stray grains.