Alumina composite coatings with enhanced high-temperature electrical insulating properties on Ni-based superalloy substrates

Electrical insulation of nickel-based superalloy substrate, especially at high temperature range, is one of the major challenges for the reliability and stability of the integrated thin-film sensors. Here, we report a solution-processed approach to fabricating high-temperature, electrically insulating coatings on Ni-based superalloy substrates. NiCrAlY coatings were fabricated by DC magnetron sputtering and heat-treated, and then Al₂O₃ films were deposited by sol-gel method. X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy were used to characterize the composition, phase, microstructure and morphology of these composite coatings. The electrical resistance of the composite coating was measured as a function of temperature up to 800 °C. Electrical resistance greater than 1 MΩ were consistently achieved from 600 °C to 800 °C. Moreover, this insulating coating survived thermal shock and thermal fatigue tests without cracking or delaminating. A type S thin-film thermocouple was prepared on the composite coating to verify its high-temperature electrical insulation performance.