Hot-pressing of translucent Y-α-SiAlON ceramics using ultrafine mixed powders prepared by planetary ball mill

Ultrafine mixed powders (D50=0.21 μm) of Si3N4, AlN, Al2O3 and Y2O3 were firstly prepared by planetary ball mill, and then were hot-pressed to fabricate translucent Y-α-SiAlON ceramics at 1650-1920 °C for 0.5 h. All the sintered samples were measured by XRD and only α-SiAlON crystalline was detected, which implies α-Si3N4 was completely transformed to α-SiAlON. It was found that a shrinkage process of the ultrafine mixed powders could be rapidly accomplished, the entire fast densification process lasted for only 5.83 min (from 1675-1850 °C at a heating rate 30 °C/min), which is much shorter than the shrinkage time needed for conventional powders (>30 min). Meanwhile, for the same infrared transmittance, the present α-SiAlON ceramics was sintered at 100-150 °C lower temperature than the reported translucent Y-α-SiAlON ceramics using conventional mixed powders. Correspondingly, holding time for the present α-SiAlON ceramics was shortened to 0.5 h, which is only half of the reported ones. The fast shrinkage, lower sintering temperature and shorter holding time may be attributed to the ultrafine mixed power employed in this paper. At the same time, all samples showed light transmission and a high, stabilized infrared transmittance (~60% for 1.2 mm thick sample) was measured for the samples sintered at 1800-1920 °C.