SiC powder compacts were prepared with Al2O3, Y2O3, and CaO powders. By two‐step sintering, fully dense nanostructured SiC ceramics with a grain sizes of ∼40 nm were obtained. The grain size–density trajectories are compared with those of conventional sintering processes.

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The sinterability of three kinds of commercially available nano-sized SiC powders and a treated nano-sized SiC powder was investigated using Al 2 O 3 -Y 2 O 3 -CaO as a sintering additive. The commercially available, as-received nano-sized SiC powders were difficult to sinter to a relative density of 95! by conventional hot pressing. The effects of the free carbon and SiO 2 impurities in the starting powders on the sinterability of the nano-sized SiC powders were identical to those on the submicron SiC powders. However, both the extremely high free carbon content and low green density of the commercially available nano-sized SiC powders were responsible for their poor sinterability. The reduction of the free carbon content by oxidation and the control of the SiO 2 content by acid treatment were beneficial for enhancing the sinterability of the nano-sized SiC powder during liquid-phase sintering.