Spark-Plasma Sintering of Silicon Carbide Whiskers (SiCw) Reinforced Nanocrystalline Alumina

The combined effect of rapid sintering by spark-plasma-sintering (SPS) technique and mechanical milling of γ-Al₂O₃ nanopowder via high-energy ball milling (HEBM) on the microstructural development and mechanical properties of nanocrystalline alumina matrix composites toughened by 20 vol% silicon carbide whiskers was investigated. SiC_w/γ-Al₂O₃ nanopowders processed by HEBM can be successfully consolidated to full density by SPS at a temperature as low as 1125°C and still retain a near-nanocrystalline matrix grain size (∼118 nm). However, to densify the same nanopowder mixture to full density without the benefit of HEBM procedure, the required temperature for sintering was higher than 1200°C, where one encountered excessive grain growth. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results indicated that HEBM did not lead to the transformation of γ-Al₂O₃ to α-Al₂O₃ of the starting powder but rather induced possible residual stress that enhances the densification at lower temperatures. The SiC_w/HEBMγ-Al₂O₃ nanocomposite with grain size of 118 nm has attractive mechanical properties, i.e., Vickers hardness of 26.1 GPa and fracture toughness of 6.2 MPa·m^1/2.