Oxidation behavior of a continuous carbon fiber reinforced ZrB2/SiC/Si3N4 composite

In this work, the oxidation behavior in air of a ZrB2 - SiC - 40% vol Cf composite has been investigated in a thermogravimetric analyzer and in a bottom-up loading furnace. A preliminary experiment was conducted in the TG analyzer from room temperature up to 1550°C in air, followed by 6 hours isothermal runs at different temperatures (800, 1000, 1200, 1400°C). In parallel, short term oxidation experiments were carried out in a bottom loading furnace at 1650°C for 1, 3, 5 min. Weight changes were measured and the oxide layer thickness was analyzed by SEM-EDS to evaluate the degree of microstructural degradation. TG experiments show that significant evolution of volatile oxides (CO) occurs between 800 and 1000°C. At higher temperature, weight loss starts to be significantly counterbalanced by weight gain due to formation of solid oxides, such as ZrO2 or liquid B2O3, leading to a partially protective kinetic behaviour. Short term tests at 1650°C confirm the good resistance to oxidation of this composite with formation of a layered scale composed of an external borosilicate coating, an intermediate ZrO2-SiO2 layer and an inner Cf-ZrO2 layer.