Damage tolerant, translucent oxide fiber/glass matrix composites

Starting out from damage-tolerant oxidic composites with carbon (C)-coated fibers, the main part of our investigations was concentrated on Nextel 440-fibers/glass matrix composites. The matrix glasses were chosen in consideration of suitable thermal expansion coefficients and optical refractive indices. The fiber pull-out is enabled by a CVD coating with boron nitride (BN). In comparison with a single BN layer, a BN/TiO2-double layer yields better mechanical and optical properties. All composites are made by means of a traditional lab method including hot pressing.Varying differences of the thermal expansion coefficients of fibers and matrix glasses (minus, zero, plus) allow the preparation of composites presenting various mechanical properties and also different damage tolerances. A composite, which is both damage-tolerant and translucent at one and the same time requires an identical thermal expansion coefficient and, in addition, an identical optical refractive index of the fibers and the matrix. Bubbles must be avoided in any case.