Tensile strength of directionally solidified chromia-doped sapphire

Tensile fracture properties of directionally solidified chromia-doped c-axis sapphire fibers have been studied in a range of temperature (room temperature up to 1400 °C) and dopant content (0, 300 ppm and 1% of Cr2O3). Delayed failure of the fibers was studied by measuring the dependence of the tensile strength on the loading rate and by fractographic studies on the fracture surfaces of the fibers. In all the temperature range, the fibers doped with 300 ppm of Cr2O3 are slightly stronger than the pure sapphire fibers. The least strong fibers are those containing 1% of Cr2O3. For this badge of material, the beneficial effect of solution hardening is counterweighted by increasing amount of defects caused by a faster fabrication. Slow crack growth appears to be the process controlling delayed failure at higher temperature. Little contribution of slow crack growth to delayed failure is found at the lower temperature.