Synergistic Effects of Oxidation and Load on SiC/BN/SiC Ceramic Matrix Composite Degradation at Intermediate Temperatures

SiC/BN/SiC ceramic matrix composites (CMCs) are desirable for use in the hot section of jet engines, where temperatures can reach 1200°C or higher. However, due to thermal gradients and backside cooling, many SiC/BN/SiC CMC components will experience intermediate temperatures ranging from 600-800°C. Oxidation mechanisms in this intermediate temperature range are not well understood. CMCs in this region will also experience micro-cracking arising from mechanical and thermal stresses, increasing pathways for oxidant ingress. The following standalone and synergistic effects of oxidation and micro-cracking on SiC/BN/SiC CMC degradation were explored:

1. The baseline oxidation mechanisms of the SiC/BN/SiC CMC in dry and wet oxygen from 400-800°C were observed without load using thermogravimetric analysis (TGA).
2. Micro-crack spacing, crack opening displacement, and micro-crack composition were quantified for a SiC/BN/SiC CMC under increasing tensile stress at room temperature and 600°C utilizing a micro-tensile stage with light and scanning electron microscopy.
3. The synergy between oxidation and applied load was determined by performing oxidation load holds in lab air, dry oxygen, and wet oxygen at 600 and 800°C. The experimental results were compared to CMC damage models.