The ultrahigh strength of carbon/carbon (C/C) composites at temperatures above 2273 K make them promising candidate materials for high temperature structural applications 1,2. However, they are oxidized when used in an oxidizing environment at high temperature, leading to a decrease in mechanical properties 3. A multi-layer protective coating, using SiC as an internal buffer layer, has been proposed 4-6 and MoSi_2, which has a high melting point and excellent oxidation resistance, could be a useful outer-layer material. However, the mismatch of thermal expansion coefficient between the MoSi_2 outer-layer and the SiC bonding layer usually leads to cracking of the MoSi_2 coating, which produces channels for oxygen attack. Therefore, pure MoSi_2 cannot be used as the outer-layer, and a multi-composition coating might be better. The toughness of MoSi_2 can be improved by adding SiC and Si 7, and the toughness of the coating can be increased by adding SiC whiskers (SiCw) 8. To date, there are no reports of using MoSi_2-SiC-Si toughened with SiCw as the coating material and such is examined here. To obtain a dense MoSi_2-SiC-Si coating with a uniform distribution of SiCw, a two-step technique was used. An inner-layer of porous SiC with distributed SiCw and a dense outer-layer of MoSi_2-SiC-Si were prepared by slurry and pack cementation, respectively. The microstructures and oxidation protection ability of the coatings were investigated.
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