SiC/SiC mini-composites with yttrium disilicate fiber coatings: Oxidation in steam

Solutions of YPO4 were used to precipitate YPO4 on pre-oxidized Hi-Nicalon-S SiC fibers. Tows of the coated fibers were then infiltrated with a preceramic polymer loaded with SiC particles to form mini-composites. During pyrolysis of the matrix, SiO2 and YPO4 on the fibers reacted and formed a Y2Si2O7 fiber matrix interphase. Mini-composites were exposed to steam at 1000 °C for 10, 50, and 100 h, tensile tested, and the effect of oxidation in steam on the functionality of the Y2Si2O7 fiber coating was investigated. The minicomposites oxidized at 1000 °C for 10 h retained 100 % of their unoxidized strength, and those oxidized for 50 and 100 h retained 92 % and 90 % of unoxidized strength, respectively. Strength retention and fiber pullout in both unoxidized and oxidized minicomposites suggests that the Y2Si2O7 interphase was effective in maintaining a weak fiber-matrix interface.