Densification of Si 3 N 4 with LiYO 2 Additive

This paper deals with the densification and phase transformation during pressureless sintering of Si 3 N 4 with LiYO 2 as the sintering additive. The dilatometric shrinkage data show that the first Li 2 O‐ rich liquid forms as low as 1250°C, resulting in a significant reduction of sintering temperature. On sintering at 1500°C the bulk density increases to more than 90% of the theoretical density with only minor phase transformation from α‐Si 3 N 4 to β‐Si 3 N 4 taking place. At 1600°C the secondary phase has been completely converted into a glassy phase and total conversion of α‐Si 3 N 4 to β‐Si 3 N 4 takes place. The grain growth is anisotropic, leading to a microstructure which has potential for enhanced fracture toughness. Li 2 O evaporates during sintering. Thus, the liquid phase is transient and the final material might have promising mechanical properties as well as promising high‐temperature properties despite the low sintering temperature. The results show that the Li 2 O−Y 2 O 3 system can provide very effective low‐temperature sintering additives for silicon nitride.