Ablation, Thermal, and Morphological Properties of SiC Fiber-Reinforced Ceramic Matrix Composites

摘要

This research encompassed the characterization of three novel Ceramic Matrix Composites (CMCs) in order to predict their performances in hypersonic applications. Ablation, thermal, and morphological properties of these CMC materials were characterized by in-situ ablation sensors, thermogravimetric analyses, and scanning electron microscopy (SEM) observations, respectively. The in-situ ablation sensor made use of four O.S mm thermocouples which were mounted into the sample at staggered depths after the sample had been micro-drilled. As the surface eroded and the recession front advanced, thermocouples would break, resulting in a unique timestamp as the front passed each one. Plotting the recession penetration as a result of these timestamps and superimposing a trendline yielded the recession rate for each material. Thermal testing proved the PyroSic? composites retain virtually all their mass when exposed to high-temperature environments, never losing more than 1.5% of their mass. The Korean CMC, on the other hand, did not perform as well, retaining only 55% of its original mass when subjected to a 5°C/min rate of temperature elevation. Higher rates of elevation tended to mitigate the loss of material. Morphological characterization aimed to compare the microstructural features before and after ablation testing. As expected, the scorched surface showed many traits indicative of prolonged thermal stress, including hairline fractures, distortions of the glass ceramic matrix, and splintering of fibers. The combination of these attributes promotes a degree of disorder into the composite, diminishing its ability to resist further thermal and mechanical stress. Moreover, at a heat flux of 1000 W/cm~2, the mean recession rates of the PyroSic? 2704 and PyroSic? 4686 samples were 0.0231 and 0.0148 mm/s, respectively, representing a difference of 56%. Although this research provides valuable insight into the properties of these CMCs, future trials will need to be conducted to confirm the results and account for statistical variance.