Hot press sintering and superplastic forming of fine-grained Si3N4-Si2N2O composites

Si3N4- Si2N2O composites were fabricated with amorphous nano-sized silicon nitride powders by the hot press sintering(HPS). The Si2N2O phase was generated by an in-situ reaction 2Si(3)N(4)(s)+1.5O(2)(g)=3Si(2)N(2)O(s)+N2(g). The content of Si2N2O phase up to 60% was accepted when the sintering temperature was 1650 degrees C and decreased whether the sintering temperature was increased or not, which indicated that the reaction was reversible. The mass loss, relative density and average grain size increased with raising of sintering temperature. The average grain size was less than 500nm if the sintering temperature was below 1700 degrees C. The sintered body crystaled completely at 1600 degrees C. The microstructure crystaled in 1600 degrees C indicated that most of the grain size was in 150-250nm. The aspect ratio of some grains reached 1.5. The superplastic deep-drawing forming could be undertaken at 1550 degrees C with a forming velocity of 0.2mm/min. The complex-shape gears could be formed by a sinter-forging technology when the sintering temperature was 1600 C and the superplastic forging temperature was 1550 degrees C.