Measurement of solute segregation in as-cast single crystal Ni-based superalloys

Detailed composition measurements using X-ray spectroscopy have been conducted in a typical third generation Ni based superalloy, CMSX10K. It is shown that the measured composition is a volume average of the fraction of γ and γ′ phases within the X-ray interaction volume. The measurements were affected by the size and distribution of the γ′ precipitates constituting the microstructure and most significantly when there is an appreciable difference in solubility limits in γ and γ′ phases for an element. These results are discussed in relation to microsegregation characterisation using the commonly used point count method. Some limitations of this latter approach are highlighted.