Transmission electron microscopy specimen preparation of ceramic coatings on ceramic fibers

A method of preparing transmission electron microscopy (TEM) specimens of coated ceramic fibers has been developed that produces large areas containing many electron transparent fibers, due to the minimal preferential milling of the epoxy matrix. Multiple individual fibers or tows are impregnated with a high-temperature epoxy and contained to assure a high fiber-to-epoxy volume ratio. The samples are then sectioned and mechanically thinned either parallel or normal to the fiber axes using a wedge polisher on diamond lapping films to achieve a thickness of less than 5 mu m The thinned sample is then ion-milled to electron transparency in less than 30 min, giving representative specimens of the coating, fiber, and coating-fiber interface. This technique is also well suited to preparing extremely flat specimens for both light microscopy and scanning electron microscopy analysis of thin coatings.