Meaning
Numerical values measure the variation in chemical composition between the dendritic cores and interdendritic regions of a cast metal. A micro-segregation index indicates the severity of element grouping that occurs during the solidification of complex superalloys. This value determines the length and temperature of the subsequent heat treatment.
Chemical Distribution
Chemical distribution is never uniform during the initial casting of single-crystal blades. Elements like rhenium and tungsten concentrate in the solidifying dendrites, while aluminum and titanium are pushed into the remaining liquid. This concentration gradient is quantified by the micro-segregation index, which must be minimized to ensure uniform properties.
Thermal Influence
High values of this metric require longer homogenization cycles at high temperatures to distribute the elements evenly. If the micro-segregation index remains high, the alloy will exhibit localized zones with low melting points. These zones are prone to premature failure during thermal processing.
Audit Standard
Aerospace quality inspectors utilize energy-dispersive X-ray spectroscopy to measure this chemical variation in sample castings. The micro-segregation index must meet strict regulatory thresholds before a supplier’s casting process can be certified for volume production. In Chinese manufacturing centers, these audit reports are submitted to the Ministry of Industry and Information Technology as part of the industrial licensing process.
This step is necessary to guarantee that the cast parts possess the required homogeneity to survive in high-stress aviation environments.
