Thermo-Mechanical Behaviour of HfO₂ Coatings for Aerospace Applications

Abstract

Abstract. The use of ceramic composite materials in aerospace applications requires the development of oxidization protection coatings which can withstand very high temperatures. HfO 2 is a promising material as a high temperature oxidization protective layer. HfO 2 coatings have been deposited by radiation frequency magnetron sputtering all over the surface of SiC substrates and were tested under re-entry conditions. Also their oxidization resistance in air in the temperature range 1100 to 1450°C has been examined. The coatings were found to be stable and well-adhering to the substrate even after 100 re-entry cycles. No oxidization of the underlying SiC structure is observed. Re-entry and oxidization tests result in the formation of HfSiO 4 at the HfO 2 /SiC interface, which further promotes their oxidization resistance.

Synthesis, Sintering, and Oxidative Behavior of HfB2–HfSi2 Ceramics

“…The presence of this silicate compound is in agreement with previous investigations related to the high-temperature oxidation of SiC containing HfB 2 -based composite systems, namely HfB 2 –20 vol % SiC and HfB 2 –26 vol % SiC w . In this regard, it should be also mentioned that the formation of HfSiO 4 at the HfO 2 /SiC interface during oxidation tests was observed to improve the oxidation resistance of the material …”

Synthesis, consolidation and characterization of monolithic and SiC whiskers reinforced HfB2 ceramics

“…26 In this regard, the formation of HfSiO 4 at the HfO 2 /SiC interface during oxidation tests conducted on HfO 2 coatings deposited on SiC substrates was observed to improve the oxidation resistance of the material. 30 Vickers hardness and fracture toughness were determined for the produced higher dense monolithic and composite samples and the results are reported in Table 1. It is seen that hardness of the whiskers-reinforced composite is not statistically different from that of the monolithic material.…”

Phase diagram up to 105 GPa and mechanical strength ofHfO2

“…Due to its excellent structural stability and dielectric properties, hafnia is a material with a wide range of industrial applications in resistant coatings 1 and in electronic materials as gate insulators. 2 Furthermore, hafnia has received attention as an oxide material with potentially superhard highpressure phases.…”