Analytical electron microscopy characterization of boron in sintered α-SiC

The final microstructure of α-SiC sintered with the addition of densification aids of elemental carbon and B4C consists of ∼8 μm α-SiC grains, large (>1 μm) B4C grains possibly containing a small amount of silicon, and free carbon (mostly graphite). The sintering of the SiC with a boron-containing phase causes the α-SiC grains to become saturated with boron. During annealing experiments and high temperature, constant stress creep experiments, small (10 to 20 nm) B4C precipitates nucleate and grow within the α-SiC grains. This precipitate formation was independent of applied stress. No boron was detected on grain boundaries in the starting material or material which had been annealed or deformed. 6 refs., 7 figs