EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

AlON transparent ceramics were fabricated by pressureless sintering starting from sub-micron AlON powders synthesized It was found that, for single phased synthetic AlON powders, there were special prisms, growth steps and pore structures on the surface and inside of the powder. Binary twin structure is ubiquitous in the synthesized powder particles. The EBSD results showed that the twin structure had the same orientation difference of {111}/60°. A large number of dislocations was accumulated around the twin boundary, and the dislocation density was about 6.023 × 10$^1$$^5$ m$^-$$^2$, whereas there was no dislocation in the region far from the twin boundary.
The effects of Y$_2$O$_3$, La$_2$O$_3$ and MgO sintering aids on the densification, microstructure and optical properties of AlON transparent ceramics were investigated. By adding 0.10 wt% Y$_2$O$_3$ + 0.20 wt% MgO and 0.16 wt% Y$_2$O$_3$ + 0.04 wt% La$_2$O$_3$, transparent AlON ceramics with clean grain boundary and uniform grain size were frabricated after sintering at 1900 °C for 24 hours. The optical transmittance at the wavelength of 1100 nm, Vickers hardness, fracture toughness and flexural strength of the AlON ceramic reached 81%, 17.59 GPa, 1.46 MPa•m$^1$$^/$$^2$ and 293 MPa, respectively. It was found by EBSD that a ternary twin crystal with a novel sandwich structure appeared in the AlON ceramics in addition to the binary twins. The misorientation of the sandwich-like twins was completely consistent with that of the twins in the powder, which is {111}/60°. It was concluded that the formation of ternary twins is to release higher internal stress. The binary twins in the ceramic were considered to be inherited from synthesized powder and would not be affected by the post-sintering conditions.