Mechanical behavior of anti-oxidation coatings on C/C composites at elevated temperature: An in-situ indentation study

Mechanical behavior of anti-oxidation coatings at high temperatures has an important influence on service safety of C/C composites. In this study, an in-situ high temperature indentation method was firstly adopted to study mechanical behavior of Hf-based anti-oxidation coatings in air up to 1000 °C. The indentation tests at room temperature, 800 and 1000 °C were conducted on the surface of the coatings. The maximum indentation depth and modulus increased and decreased with increasing temperature, respectively. And they both changed at a slower rate ranging from room temperature to 800 °C and a faster rate ranging from 800 to 1000 °C. It is also found that a smooth thin glass layer was formed on the surface of the coatings and had little influence on the mechanical behavior of the coatings at 800 °C. However, the oxidation became severe and some voids came into being at 1000 °C. The mechanical behavior was seriously affected, and the plasticity was obviously enhanced, resulting in a significant reduction in the modulus of the coatings.