Nitridation mechanism of Si compacts studied by transmission electron microscopy

Microstructures of reaction-bonded Si3N4 bodies, which were fabricated at 1623 K, have been studied to identify the nitridation mechanism of Si compacts by transmission electron microscopy. The percent nitridation of the Si compacts gradually increases with increasing reaction time. In the sample nitrided for 36 ks, the residual Si particles showing a sharped-shape contain many cracks and fine-sized alpha-Si3N4 grains around the cracks, whereas the morphology of residual Si particles in the sample nitrided for 72 ks, shows an island shape due to the nitridation, and high-density of dislocations and microcracks are observed. The sample nitrided for 108 ks is constructed with typical net-shape having about 0.4 mu m fine grains. Cracks and dislocations in the Si particles play an important role to explain the nitridation mechanism of Si compacts.