Extraction replication studies of near-surface microstructures in laser-drilled samples of the powder metallurgy Ni-based superalloy IN100

Hybrid extraction replication has been used to prepare TEM samples from laser-drilled coupons of the Ni-based superalloy IN100. In addition to extracting the inert carbide and boride particles, these carbon replicas reveal the microstructure of the surrounding metallic phases allowing the particle distribution to be studied. It is shown that the IN100 base metal contains large (> 100 nm) MC, M23C6 and M3B2 particles, consistent with previous TEM studies on this alloy. In the recast layers on the interior surfaces of the laser-drilled holes, however, dendritic micro-segregation in the supersaturated γ phase gives a cellular sub-structure, and the inert particles observed are nano-scale Ti-rich MC-type carbides at the cell boundaries. The replicas also reveal that the base metal/recast interface is abrupt. These observations illustrate the power of the hybrid replication technique for revealing variations in nano-scale features over much larger length scales (≫ 10 μm).