Characterization of the reaction products that develop in the processing of Al2O3/BaZrO3 laminated composites

Abstract The absence of a chemical reaction at an interface is conventionally thought to be an important criterion in producing a tough ceramic matrix composite (CMC). As a result of this criterion, interphases in CMCs were chosen on the basis of their chemical reactivity. A weak interface results in crack deflection, crack bridging, and, in fiber-reinforced ceramics, fiber pullout, resulting in an increased fracture toughness. In this paper, we present microstructural observations on alumina (Al 2 O 3 )–barium zirconate (BaZrO 3 ) laminated composites wherein the reaction products that develop during processing resulted in sharp interfaces and appear to be weak enough to deflect cracks. These in situ reaction products in Al 2 O 3 –BaZrO 3 laminated composites were characterized with the use of a scanning electron microscope, an electron microprobe, and a transmission electron microscope. The phases that develop, ZrO 2 , BaO·Al 2 O 3 , and BaO·6 Al 2 O 3 , produced sharp interfaces and are arranged in a sequence that could be predicted by using information from the phase diagram.