Oxidation-resistant fiber coatings and related methods

A method of manufacturing Ceramic Matrix Composites with an in-situ rare earth silicate-coated reinforcing fiber, the method comprising:

• pre-oxidizing a plurality of fibers, wherein the fibers are selected from the group consisting of SiCO fibers, SiCN fibers, SiCNO fibers, SiBCN fibers;
• coating the plurality of pre-oxidized fibers with a rare earth orthophosphate (REPO4), wherein the rare earth orthophosphate (REPO4) is selected from the group consisting of YPO4, ScPO4, CePO4, PrPO4, NdPO4, PmPO4, SmPO4, EuPO4, GdPO4, TbPO4, DyPO4, HoPO4, ErPO4, TmPO4, YbPO4, and LuPO4, or combinations thereof;
• forming a fiber tow, or fiber cloth preform with the REPO4 coated fibers;
• infiltrating the preform with a preceramic precursor with filler particles to form a Ceramic Matrix Composite;
• curing and pyrolizing the ceramic matrix composite;
• repeating the coating, infiltrating, curing and pyrolizing steps to increase ceramic matrix composite density;
• performing a heat treatment of the ceramic matrix composite in an inert environment of nitrogen or argon at about 1000-1500 degrees Celsius for about 5 minutes to about 100 hours to convert the REPO4 coatings on the fibers to rare earth disilicate coatings.