Superplasticity and sinter-forging of fine-grained Si₃N ₄-Si₂N₂O composite

The Si₃N₄- Si₂N₂O composites are fabricated with amorphous nano-sized silicon nitride powders by the liquid phase sintering(LPS) method in this article. XRD analysis shows that the sintered body consists of β-Si₃N₄ and Si ₂N₂O. SEM experiment conforms that the average grain size of sintered body is less than 300nm. The superplastic deep-drawing forming can be proceed at a low temperature of 1550°C with a punch velocity of 0.2mm/min. There are only a few small sintered defects before forming, but there are a lot of cavity groups after forming. Cavitation failure occurs by nucleation, growth and interlinkage of cavities. The complex-shape gears can be formed by a sinter-forging technology when the sintering temperature is 1600°C and the superplastic forging temperature is 1550°C.