Role of immiscible and miscible second phases on the sintering kinetics and microstructural development of nano-crystalline α-Al2O3-based materials

An ultra-fine alumina powder was doped with yttrium or zirconium chloride to produce Al2O3–5 vol.%ZrO2 (AZ-5) and Al2O3–5 vol.%YAG (AY-5) composite powders. Composite samples and pure alumina, used as a reference, were submitted to dilatometric analyses up to 1500–1550 °C at 2, 5 and 10 °C/min for supplying the data required for the modeling of their sintering behaviour. The best fit for the three samples was obtained by applying an Avrami–Erofeev nucleation and growth model (An) and a subsequent power law reaction (AnFn). The evolution of the activation energy with densification is given for the three samples, as well as the prediction of their best sintering conditions. Finally, densification mechanism for the immiscible (AZ-5) and miscible (AY-5) systems are hypothesized and correlated with their final microstructures.