High temperature electrical insulation and adhesion of nanocrystalline YSZ/Al2O3 composite film for thin-film thermocouples on Ni-based superalloy substrates

• The crystallization of Al 2 O 3 matrix was inhibited by t-ZrO 2 nanocrystalline. • Large angle grain boundary and micro cracks were significantly reduced. • The electrical resistivity of the film was 10 8 Ω·cm at 1000 °C. • The lifetime of the film exceeded 48 h under high temperature thermal cycling. Electrical insulation and adhesion are two vital aspects for the integrated thin film sensors with Ni-based superalloy substrates. In this paper, nanocrystalline yttria-stabilized zirconia/alumina (YSZ/Al 2 O 3 ) composite film was fabricated on Ni-based superalloy substrate by reactive magnetron sputtering. The X-ray diffraction and scanning electron microscope results show that tetragonal zirconia (t-ZrO 2 ) nanocrystalline is homogeneously dispersed in the amorphous Al 2 O 3 matrix. The crystal size of the t-ZrO 2 nanocrystalline is well maintained with the temperature up to 1000 °C. The resistivity of the film is about 10 8 Ω·cm at 1000 °C, which is three orders of magnitude higher than that of the pure Al 2 O 3 film. Furthermore, this YSZ/Al 2 O 3 film demonstrates superior toughness and adhesion with the Ni-based superalloy substrate even after undergoing high-temperature cycles. Finally, a S-type thin-film thermocouple was fabricated on the YSZ/Al 2 O 3 film shows good stability, repeatability, and linearity in multiple thermal cycling tests up to 900 °C exceeded 48 h.