On the two‐step sintering of fine‐grained alumina ceramics using gel‐casted Sumitomo powders

Abstract Two‐step sintering (TSS) has been invented for 25 years. Its applicability to various ceramic and metallic materials has been demonstrated, yet mostly for lab‐scale fine powders and for dry‐pressed green bodies. For alumina, which is one of the most important engineering ceramics, more systematic studies on TSS of commercial fine powders are needed. In our recent work, we reported such data using gel‐casted Taimei powders TM‐DAR and demonstrated the effect of TSS on refining the microstructure. Here we seek to extend the study to gel‐casted Sumitomo powders AES‐11. Sumitomo AES‐11 is produced and used with larger quantities and at a lower cost than Taimei TM‐DAR; thus, the study of TSS would be of great technological interests. We show that for fully densified samples, TSS, one‐step high‐temperature sintering with typical holding time of 2 h, and one‐step low‐temperature sintering with a prolonged holding time of 20 h yield comparable grain sizes and mechanical properties. Our work suggests that TSS works better for the systems with high sinterability, such as those reported for nanopowders in the literature. Its extension to more engineering‐focused, cost‐sensitive applications using low‐sinterability powders is more challenging and remains to be explored.