Effect of alumina restraints on the stability of tetragonal zirconia in alumina-zirconia composite powders

Zirconia-alumina composite powders were prepared by a method of spray-drying mixed oxalate complex solutions. The prepared powders are highly homogeneous and the stability of tetragonal zirconia is greatly enhanced by the alumina restraints surrounding the zirconia particles. Higher alumina contents lead to retarded grain growth of tetragonal zirconia and the enhanced critical size for the phase transformation from tetragonal to monoclinic. The effect of alumina surroundings is explained with a simple zirconia particle-alumina shell model.