Fast pressureless sintering of highly transparent AlON ceramics by reducing Y enrichment with nano-sized granular Y2O3 as additive

Employing nano-sized granular Y2O3 (NGY) as additive, AlON ceramics with transmittance >= 80% across wavelengths at 380-4150 nm were successfully fabricated via pressureless sintering at 1880 degrees C for 2.5 h, the dwelling duration is much shorter than the >= 7 h reported in literature. The distribution of Y2O3 in starting mixtures, along with phase transformation, microstructure evolution and densification process of the samples during heating were thoroughly studied to reveal the fast densification mechanism. Local enrichment of Y2O3 in the AlON/Y2O3 mixtures was significantly reduced when using NGY instead of micro-sized lamellar Y2O3. The reduction of excessive local Y2O3 concentration resulted in less alpha-Al2O3 was decomposed from AlON during heating, and further suppressed local aggregation/coarsening at <= 1600 degrees C. The excellent microstructure obtained at early stage of sintering, together with the improved effective Y2O3 concentration in whole sample led by the decrease in local Y2O3 enrichment accelerate the densification process of AlON.