SINTER FORGING OF ZIRCONIA-TOUGHENED ALUMINA

Sinter forging experiments have been carried out on powder compacts of zirconia toughened alumina (ZTA) Ceramics Alumina-15 wt% zirconia was prepared by a gel precipitation method and calcined at temperatures o f 900 or 1100-degrees-C. Full densification of ZTA ceramics was obtain ed within 15 min at 1400-degrees-C and 40 MPa. A homogeneous microstru cture can be observed with an alumina grain size of 0.7 mum and a zirc onia grain size of 0.2 mum. Almost no textural evolution occurred in t he microstructure. During sinter forging the densification behaviour o f the compacts was improved by an effective shear strain, for which va lues of more than 100% could be obtained. As a result of the shear def ormation the densification of ZTA in the alpha alumina phase stage shi fted to lower temperature. During pressureless sintering the theta to alpha alumina transformation temperature was dependent of the precedin g calcination temperature, while during sinter forging this phase tran sformation was independent of calcination temperature and took place a t a lower temperature.