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

Mg-doped sialon ceramics with the composition of M0.4Si10.2Al1.8O1N15 were fully densified by hot pressing at 1850 degrees C for 1 h, using 0.5 wt.% MgF2 or CaF2 as a sintering additive. Densification behavior, phase assemblage, microstructure, and mechanical and optical properties were investigated in detail. The addition of fluorides, especially MgF2, 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 beta-sialon. Both the samples possessed high hardness (similar to 20 GPa) and fracture toughness (similar to 4.2 MPa m(1/2)). The CaF2-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 alpha-sialon. (C) 2017 Elsevier Ltd. All rights reserved.