Pretreatment effects on the morphology and properties of aluminum oxide thermally grown on NiCoCrAlY

Abstract

This report is part of the investigation on thin film temperature sensors for turbine blade applications. The effect of pretreatments on the morphology and properties of aluminum oxide thermally grown from NiCoCrAlY was investigated. The goal was to optimize process steps to produce a highly adherent, continuous, and insulating aluminum oxide. Two pretreatments were carried out, one in vacuum (-10^-4 Torr) at 1350 K for 5 h, and the other consisting of deposition of a 1 µm thick Al₂O₃ film by ARE (activated reactive evaporation). Samples were subsequently oxidized thermally at 1000°C for 50 h at 0.5 Torr oxygen pressure. The two pretreatments were carried out on electron-beam evaporation NiCoCrAlY, -120 μm thick, deposited on a superalloy turbine blade substrate. The results showed that the thermally grown oxide was significantly different in microstructure, surface topography and in its adherence to the NiCoCrAlY for the two pretreatments. Optimum results were obtained by combining the two pretreatments to produce an adherent, continuous, and insulating oxide film on the NiCoCrAlY coated superalloy substrate.