Densification behavior, microstructure, mechanical and optical properties of Mg-doped sialon with fluoride additives

Abstract Mg-doped sialon ceramics with the composition of M 0.4 Si 10.2 Al 1.8 O 1 N 15 were fully densified by hot pressing at 1850 °C for 1 h, using 0.5 wt.% MgF 2 or CaF 2 as a sintering additive. Densification behavior, phase assemblage, microstructure, and mechanical and optical properties were investigated in detail. The addition of fluorides, especially MgF 2 , not only resulted in more high-temperature liquid by promoting the dissolution of more N and other constituents but also reduced the viscosity of liquid due to the terminal effect of fluorine. Consequently, the densification was effectively improved. Additionally, the fluoride addition facilitated the formation of a small amount of β-sialon. Both the samples possessed high hardness (∼20 GPa) and fracture toughness (∼4.2 MPa m 1/2 ). The CaF 2 -added sample exhibited higher infrared transmittance than its counterpart due to less residual glass phase. The present work implies that fluorides are also very effective sintering additives for densifying α-sialon.