Spark plasma sintering of silicon nitride using nanocomposite particles

- Nanocomposite particles were successfully prepared using a mechanical treatment.
- Highly dense Si3N4 ceramics were obtained using nanocomposite particles and SPS.
- The shrinkage behavior of the Si3N4 with SPS depended on the presence of the sintering aids.

The spark plasma sintering (SPS) of silicon nitride (Si3N4) was investigated using nanocomposite particles composed of submicron-size α-Si3N4 and nano-size sintering aids of 5 wt% Y2O3 and 2 wt% MgO prepared through a mechanical treatment. As a result of the SPS, Si3N4 ceramics with a higher density were obtained using the nanocomposite particles compared with a powder mixture prepared using conventional wet ball-milling. The shrinkage curve of the powder compact prepared using the mechanical treatment was also different from that prepared using the ball-milling, because the formation of the secondary phase identified by the X-ray diffraction (XRD) method and liquid phase was influenced by the presence of the sintering aids in the powder compact. Scanning electron microscopy (SEM) observations showed that elongated grain structure in the Si3N4 ceramics with the nanocomposite particles was more developed than that using the powder mixture and ball-milling because of the enhancement of the densification and α-β phase transformation. The fracture toughness was improved by the development of the microstructure using the nanocomposite particles as the raw material. Consequently, it was shown that the powder design of the Si3N4 and sintering aids is important to fabricate denser Si3N4 ceramics with better mechanical properties using SPS.

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