Precipitation mechanism and microstructural evolution of Al2O3/ZrO2(CeO2) solid solution powders consolidated by spark plasma sintering

Abstract

It is difficult to synthesize Al2O3/ZrO2 solid solution because of its low solubility under equilibrium solidification conditions. In this work, a new combustion synthesis combined with water atomization (CS-WA) method was developed to prepare supersaturated Al2O3/ZrO2(CeO2) solid solution powders. The ultra-high cooling rate supplied by CS-WA greatly extends solid solubility of Al2O3 in ZrO2. The precipitation mechanism of solid solution was investigated by systematic heat treatments. The initial temperature of the metastable phase decomposed into Al2O3 and ZrO2 is 1050 °C, and it could be completely precipitated at 1400 °C in 0.5 h. The precipitated ZrO2 particles were uniformly dispersed in Al2O3 matrix and grew into submicron scale at annealing temperature of 1450 °C. Subsequently, together with detailed microstructure, phase composition, as well as mechanical properties were collaboratively outlined to discuss spark plasma sintering (SPS) behavior. The solid solution precipitated Al2O3 matrix and ZrO2 particles during the SPS process. Partial ZrO2 particles were uniformly distributed within Al2O3 matrix, while the residuary ZrO2 located at the grain boundaries and formed special transgranular/intergranular structure. The average size of nanoscale transgranular ZrO2 particles was only ∼11.5 nm. The compact ZrO2 toughened Al2O3 nano ceramic (N-ZTA) exhibits excellent mechanical properties. This work provides a guidance to produce nanostructured ZTA with high performance.