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 degrees C. The indentation tests at room temperature, 800 and 1000 degrees 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 degrees C and a faster rate ranging from 800 to 1000 degrees 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 degrees C. However, the oxidation became severe and some voids came into being at 1000 degrees C. The mechanical behavior was seriously affected, and the plasticity was obviously enhanced, resulting in a significant reduction in the modulus of the coatings.