Effect of SiC whiskers on the microstructure and oxidation protective ability of SiC-CrSi₂ coating for carbon/carbon composites

To prevent carbon/carbon (C/C) composites from oxidation, a SiC-CrSi₂ protective coating toughened with SiC whiskers (SiCw) has been prepared by a two-step technique of slurry and pack cementation. SEM and XRD analysis show that with the SiCw content increasing from 0 to 20 wt.%, the coating thickness is reduced from 420 to 100 μm, and the CrSi₂ proportion in the coating first increases and then decreases. Oxidation tests in the range 1473-1773 K shows that the coating toughened with 15 wt.% SiCw possesses a better oxidation protective ability because of its more suitable thickness and microstructure. As the oxidation temperature increases from 1473 to 1773 K, the oxidation protective ability of the coating improves gradually. The weight loss of the coated samples is primarily due to the reaction of C/C matrix and oxygen diffusing through the cracks in the coating.