Two-step sintering of AlON transparent ceramics with good mechanical properties

Two-step sintering (TSS) method was widely used to prepare fine grained ceramics with high density, smaller grain, and more uniform microstructure, which improved the mechanical properties of ceramics. AlON transparent ceramics with good mechanical properties were prepared successfully by TSS method. The TSS process includes steps at a high temperature T 1 and then at a low T 2 . The grain size of ceramics gradually increased with the increase of T 1 . When T 1 was between 1900 °C and 1930 °C, the relative densities of AlON ceramics exceeded 98 % with the grain size less than 20 μm. The effects of T 2  = 1800 °C for various holding time (12–16 h) were also investigated. The grains increased slightly with the increase of holding time. Compared with conventional pressureless sintering (CS), TSS was more beneficial to regulate grain size with better properties. The grain size decreased from 118 μm (CS) to 53.7 μm (TSS), resulting in good in-line transmittance (81.7 % at 1500 nm with 2 mm thickness). The hardness and the flexural strength via TSS is 17.36 GPa and 368 MPa, which is increased by 5 % and 20 % respectively. TSS paves a potential path to improve mechanical properties of AlON transparent ceramics.