Fracture characteristics of single crystal and eutectic fibers

Abstract

This chapter reports the results of experiments aimed at identifying the sources of high levels of strength retention and creep resistance in a two-phase A1203/Y3A15012 eutectic system. Single-crystal fibers are making new inroads into ceramic applications as active devices and are equally important for structural ceramic components as load-bearing applications. This chapter examines the fracture characteristics of single-crystal fibers from a variety of crystal systems including the Al2O3/Y3Al5O12 eutectic. The Young moduli of (0001) Al2O3, (111) Y3Al5O12, and (111) Y2O3 fibers were 453, 290, and 164 GPa, respectively. Single crystals of (111) Y2O3 were the weakest fibers and their strength did not exceed 700 MPa. The moderate tensile strength of single-crystal (111) Y3Al5O12 was controlled by the facet-forming tendency of the cubic garnet structure and in some cases by the precipitation of cubic perovskite phase YAlO3. High-strength single-crystal (0001) Al2O3 fibers did not retain their strength at elevated temperatures. The results showed that single-crystal (0001) Al2O3 failure was dependent on slow crack growth at elevated temperatures. The high-temperature tensile strength of Al2O3/Y3Al5O12 eutectic fibers was superior to sapphire and demonstrably less prone to slow crack propagation.