Preparation and Properties of HfO<sub>2</sub>-Y<sub>2</sub>O<sub>3 </sub> Composite Coating on the Surface of Iridium Coating

A “ball milling mixing–low temperature sintering–ball milling smashing” method was applied to produce fine HfO 2 -Y 2 O 3 composite powders (content of Y 2 O 3 was 7.5 wt.%). The mean diameter of powders was about 0.2μm. By using these powders as raw material, after five cycles of “electrophoresis deposition (EPD)–sintering”, a layer of about 20μm thick HfO 2 -Y 2 O 3 (HYO) composite coating was prepared on the surface of iridium (Ir) coating. The result showed that HYO coating could endure thermal shock for 3 times from 1250°C to 25°C, its emissivity was 0.69 at 400°C and its thermal diffusivity was 0.592mm 2 /s, which will be a promising candidate applied on the nozzles and wing leading edges of hypersonic vehicles.