In situ Y2Si2O7 coatings on Hi-Nicalon-S SiC fibers: Phase formation and fiber strength

Y2Si2O7 coatings were formed on Hi-Nicalon-S SiC fibers by reaction of solution-derived YPO4 coatings with glass SiO2 scales formed by fiber oxidation. Two oxidation methods were used: pre-oxidation, where fibers were oxidized prior to YPO4 coating, or post-oxidation, where fibers were first coated with YPO4 and then oxidized. Fibers with YPO4/SiO2 films were heat-treated in argon at 1200 degrees C for 20 hours to react YPO4 and SiO2 to Y2Si2O7. The effects of SiO2 to YPO4 film thicknesses on fiber strength and on the Y(2)Si(2)O(7)formation kinetics were investigated. An optimized process to obtain single-phase continuous Y2Si2O7 coatings on Hi-Nicalon-S fibers with low loss in fiber strength is suggested.