CHEMICAL-STABILITY, MICROSTRUCTURE AND MECHANICAL-BEHAVIOR OF LAPO4-CONTAINING CERAMICS

The use of LaPO4 as a weak interface in composites for high temperatur e applications was investigated using tape-cast laminates and fiber mo del systems. Three laminates were fabricated with LaPO4 as one compone nt and Al2O3, Y3Al5O12 or LaAl11O18 as the other. The chemical compati bility between the different components of the laminates, as well as t he mechanical responses to flexural deformation and the propagation of indentation cracks, were examined. Two fiber model systems (Al2O3 fib er/LaPO4 coating/Al2O3 matrix and Y3Al5O12 fiber/LaPO4 coating/Al2O3 m atrix) were studied by fiber pushout tests to measure the interfacial shear strengths. The interfacial shear strengths were calculated by th e linear and shear-lag approaches for different embedded fiber lengths . The results suggest that Y3Al5O12 fiber-reinforced composites with L aPO4 coatings have potential as high temperature materials in oxidizin g environments.