Effect of composition on phase assemblage, microstructure, mechanical and optical properties of Mg-doped sialon

Mg-doped sialon (Mgm/2Si12−m−nAlm+nOnN16−n) ceramics with different compositions of m=2n=0.6, 0.84, 1.0, 1.2, 1.6 were hot pressed at 1850°C for 1h. Phase assemblage, microstructure, mechanical and optical properties of these samples were investigated. All samples achieved/approached full densification. However, the densification of Mg-doped sialon ceramics with higher MgO/AlN content becomes more difficult. Additionally, the anisotropic growth of β-sialon grains was significantly inhibited. The unique characteristics of Mg-doped sialon ceramics intrinsically derive from the formation of Mg-containing AlN polytypoids, which consumed most of the high-temperature liquid. Furthermore, their high stability at high temperatures accounts for the difficulty in preparing single-phase Mg-α-sialon., The hardness of these samples gradually increases while indentation fracture toughness gradually decreases with increasing m=2n value. Due to little residual glassy phase, high infrared transparency/translucency was more readily achieved in Mg-doped sialon. The m=1.2 sample possesses the maximum transmittance of ∼50% at ∼2μm.