Sintering Behaviour of AI₂O₃-ZrO₂ Microcomposites Prepared by a Combined Gel-Precipitation Route

Abstract

AI₂O₃-ZrO₂ microcomposites having nominally equal volumes of the two phases were prepared by a combined gel-precipitation technique using AICI₃ and ZrOCI₂ precursors. Dried gel powders were calcined at 375°C followed by compaction and sintering to study the (i) evolution of phases of AI₂O₃ and ZrO₂and (ii) densification behaviour of the microcomposites. ZrO₂ crystallized to tetragonal/cubic structure formed at 375°C, while AI₂O₃ crystallized to δ-AI₂O₃not before 1000°C and converted to α-AI₂O₃at or above 1200°C.

For sintering time of 4 h the density increased almost linearly from about 74% of the theoretical at 450°C to 94% at 1150°C and then gradually to a maximum of 97% at 1400°C. All the zirconia was in the tetragonal form up to 1000°C, but the tetragonal fraction decreases from 97% at 1100°C to 10% at 1400°C.

Sintering studies for varying holding times (4 h to 10 h) at temperatures from 1150° to 1250°C showed that the density increased, but the tetragonal fraction decreased with increasing temperature and with holding time at a given temperature. At 1200°C, the tetragonal fraction was 52% and the density was 97% of the theoretical. Scanning electron microscopy showed that the AI₂O₃ and ZrO₂ phases were intimately mixed with average grain size of each phase less than 500 nm.