Microstructural characterization of a zirconia-toughened alumina fiber reinforced niobium aluminide composite

An NbAl₃ + Nb₂Al composite reinforced with continuous zirconia-toughened alumina, PRD-166 fibers, was produced by pressure casting and was examined by optical and transmission electron microscopy and energy dispersive spectroscopy. Exposure of the fiber to the molten metal resulted in ZrO₂ and Al₂O₃ grain growth, formation of a thin layer of an amorphous phase on the grain boundaries of Al₂O₃ and transformation of ZrO₂. Preferential Al₂O₃ grain growth near the surface of the fiber led to the rejection of ZrO₂ from this region into the molten metal. In NbAl₃ slip occurred by the glide of a<110] superdislocations and tolesser extent by the glide of a pair of <111 + <311] dislocations on the (112) planes and a/2<110] superpartial dislocations on the (001) plane. The operating slip system in Nb₂Al was identified as {010)<100]. a<100] dislocations were dissocaited into ax<100] partial dislocations joined together by a stacking fault.