Zirconia toughened aluminas by hydro-thermal processing

Zirconia toughened alumina materials have been produced by a hydro-thermal powder synthesis route. The resultant sols were concentrated using filtration to form extrudable pastes. The extruded products when dried and sintered had uniform microstructures with improved mechanical properties compared to pure mono-phase rods produced by a similar route. The zirconia particles produced by hydro-thermal synthesis were too small to give the optimum toughening effect, as the zirconia phase is undoped. Two alternative methods were investigated in order to increase the zirconia grain size in the finished body. The hydro-thermally synthesized zirconia was freeze-dried to increase the flock size before mixing with the alumina sol and a commercial monoclinic zirconia powder was added to the alumina sol prior to concentration. The improvements in mechanical performance correlated well with theoretical predictions.