Fast densification mechanism of highly transparent AlON ceramics pressureless sintered by co-doping Y2O3 and MgO additives

By co-doping 0.15 wt% Y 2 O 3 and 0.60 wt% MgO , AlON ceramics with high transmittance in visible and infrared range (the maximum transmittance of 81.8%@3600 nm, 78.1%@400 nm) were successfully fast fabricated via pressureless sintering at 1880 °C for 2.5 h. The phase assemblage, microstructure and densification process of samples doped (Y 2 O 3 /MgO single- and co-doped) and undoped additives during heating were monitored to explore the densification mechanism. MgO was found to be an exceptional inhibitor for both AlON decomposition and grain growth. By incorporating MgO as one constituent of additives, the content of α-Al 2 O 3 that decomposed from AlON in samples during heating was significantly reduced and Mg 2+ illustrated inhibition to grain boundary migration, resulting in particle aggregation/coarsening were effectively suppressed at ≤ 1600 °C. Based on the obtained microstructure with compacted small particles and negligible particle aggregation/coarsening at early stage of sintering, facilitated by the acceleration of Y 3+ on mass transfer, rapid densification of AlON was achieved.