CHARACTERIZATION OF THE REACTION-PRODUCTS THAT DEVELOP IN THE PROCESSING OF AL2O3 BAZRO3 LAMINATED COMPOSITES/

The absence of a chemical reaction at an interface is conventionally t hought to be an important criterion in producing a tough ceramic matri x composite (CMC). As a result of this criterion, interphases in CMCs were chosen on the basis of their chemical reactivity. A weak interfac e results in crack deflection, crack bridging, and, in fiber-reinforce d ceramics, fiber pullout, resulting in an increased fracture toughnes s. In this paper, we present microstructural observations on alumina ( Al2O3)-barium zirconate (BaZrO3) laminated composites wherein the reac tion products that develop during processing resulted in sharp interfa ces and appear to be weak enough to deflect cracks. These in situ reac tion products in Al2O3-BaZrO3 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 . Al2O3, and BaO . 6 Al2O3, produced sharp interfaces and are a rranged in a sequence that could be predicted by using information fro m the phase diagram. (C) Elsevier Science inc., 1998.