Carbothermal Synthesis of Al‐O‐N Coatings Increasing Strength of SiC Fibers

Non‐bridging Al‐O‐N coatings have been synthesized on the surface of Tyranno ZMI SiC fibers by a low‐cost carbothermal nitridation method. First, a nanoporous carbide‐derived carbon (CDC) layer is produced on the surface of SiC fiber by the extraction of Si with chlorine; the CDC layer on the fiber is then infiltrated by AlCl 3 solution, and finally nitrided in ammonia at atmospheric pressure to produce the coating. The intermediate carbon layer acts as a template for the coating, facilitates the formation of aluminum oxynitride, and helps to build a strong bonding between the fiber and coating. Optimization of the process parameters led to a more than 65% improvement in the tensile strength (up to ∼5.1 GPa) and a three‐time increase in the Weibull modulus for the fiber with 200 nm coating compared to the as‐received fibers. The coated fiber exceeds the strength of all other small‐diameter SiC fibers reported in the literature. Al‐O‐N coating may also provide oxidation protection for the fibers in high‐temperature applications.