Characterization of interfacial reaction products in alumina fiber/barium zirconate coating/alumina matrix composite

Abstract

Barium zirconate (BaZrO 3) is a candidate material for interface engineering of alumina fiber/alumina matrix composites. Al 2O 3 and BaZrO 3 react at high temperatures to form a series of reaction products. The objective of this work was to characterize these reaction products and to investigate their effect on crack propagation. BaZrO 3 coating was applied on Al 2O 3 fibers via a sol–gel route. The characterization was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The reaction products between BaZrO 3 coating and Al 2O 3 (fibers and/or matrix) included ZrO 2, barium monoaluminate (BaO·Al 2O 3) and Ba β-Al 2O 3 (BaO·7.3Al 2O 3). In hot-pressed composites, barium aluminate was mainly present in the form of Ba β-Al 2O 3. The Ba β-Al 2O 3 is known to have a layer-type structure, which is likely to be propitious for crack deflection. The interfacial reactions are diffusion-controlled solid-state processes, mainly depending on the diffusion of Ba cations. The Ba β-Al 2O 3 phase can form either through direct reaction between the BaZrO 3 coating and Al 2O 3 or through indirect reaction between a BaO·Al 2O 3 intermediate phase and Al 2O 3. The BaZrO 3 coating and the reaction products between the coating and fiber/matrix provide multiple weak interfaces, which are likely to result in crack deflection and thus toughness enhancement in an all oxide composite.