Effects of surface finish of single crystal superalloy substrate on cyclic thermal oxidation of its nanocrystalline coating

• Surface finishing of substrate alloy affects oxidation of nanocrystalline coating.
• Scale rumples only on nanocrystalline coating deposited on sand-blasted substrate.
• Scale spalls off layer-by-layer on coating deposited on sand-blasted substrate.
• Scale fractured on coating deposited on polished or ground substrate.

Cycling oxidation behavior of the nanocrystalline coating on the N5 superalloy substrate of different surface finishing is investigated at 1050 °C. Results indicate that the surface finishing of the alloy substrate affects oxidation behavior of the sputtered nanocrystalline coating. After cyclic oxidation, oxide scale on the nanocrystalline coating rumples heavily and spalls off following a way of layer-by-layer in case that the alloy substrate is pretreated by sand blasting. However, it just roughens rather than rumples when the alloy substrate is pre-polished or ground by 2000# SiC paper and its spallation follows a way of bulk fracture.