Boron carbide-titanium diboride composites are fabricated by reactively sintering boron carbide with titanium in the hot-press. Sintering behavior and microstructural development of the composites are being studied by analytical and high-resolution transmission electron microscopy. Kinetics of the phase formation is being investigated by interrupted growth studies at a wide temperature range. Fracture toughness data are correlated with microstructure and phase composition.

Our objective in this project is to identify oxidation modes of nonoxide particles or fibers that are embedded in a ceramic matrix and determine the dependence of such modes on the composition and microstructure of the matrix. A model is being developed, based on oxygen diffusion rates in matrix and in oxidation products. Experimental measurements (by TEM) of oxide thickness around particle vs. depth of particle below composite surface can be predicted by the model. The matrix can be modified to control oxidation behavior of the embedded reinforcements.

Ceramic matrix composites based on several different oxide matrix materials and reinforced with silicon carbide platelets are prepared by sintering and hot-pressing techniques in an effort to obtain strong, tough, and dense materials. Densification behavior of mullite, alumina, and other matrices is examined. Fracture toughness and strength are measured and related to the microstructure, particularly the interface characteristics.

Boron nitride-carbon powder mixtures are being sintered by hot-pressing at temperatures up to 2200°C. The effect of BN crystallinity on the possible formation of compounds and graphitic solid solutions is investigated by high-resolution transmission electron microscopy.