Transmittance improvement of Dy–α-SiAlON in infrared range by post hot-isostatic-pressing

At present stage, the transmittance improvement is still a thorny problem in SiAlON ceramics due to their complex composition and processing. In the present research, Dy–α-SiAlON ceramics were selected to be translucent in the medium infrared range. The samples had a higher densification value by using hot-pressing (HP) sintering method at 1650–1700 °C with or without LiF additive. The as-sintered specimens experienced the post-hot-isostatic-pressing (PHIP) treatment at 1650–1700 °C for 30–90 min in either N2 or Ar environment to increase the optical transmittance. A significant optical transparency improvement has been found in Dy–α-SiAlON, with or without LiF co-doping, undergone a PHIP at 1700 °C for 30 min under an Argon gas pressure of 180 MPa. The improved transmittance attributes to a fully developed α-Sialon crystalline phase, a uniform grain size, a denser grain arrangement, and a clean grain boundary, based on the X-ray diffraction analysis, SEM and TEM microstructure observation, and optical transmittance measurement.