Stereological characterization of γ′ phase precipitation in CMSX-6 monocrystalline nickel-base superalloy

The purpose of this investigation was to study in detail the means to quantitatively evaluate γ′ phase precipitation. Many of the mechanical properties of superalloys are directly influenced by the presence of the γ′ (gamma prime) precipitate phase dispersed in a γ matrix phase. The γ′ precipitates act as effective barriers to dislocation motion and restrict plastic deformation, particularly at high temperatures. Due to this, it is essential to accurately quantify the γ′ precipitate size, volume fraction and distribution. Investigations based on quantitative metallography and image analysis were performed on a monocrystalline nickel-base superalloy taking into consideration various γ′ precipitate sizes present in that alloy microstructure. The authors of the present paper propose a new method of quantifying the total volume fraction of the γ′ phase applying images of the microstructure with γ′ phase precipitates registered using light microscopy, scanning electron microscopy (at two different magnifications) and scanning transmission electron microscopy.