Influence of processing and microstructure on mechanical properties in Sialon-based ceramics

The influence of processing and microstructure on the mechanical properties of Sialon-based ceramics, in-situ self-toughening induced by heat treatment and second-phase toughened, was investigated. Three kinds of Sialon-based ceramic materials were covered in the research: 1. TiB(p), MoSi2(p), SiC(p), and SiC(w) second-phase reinforced Sialon materials; 2. alpha/beta-double-phase-Sialon ceramics, using rare earth oxides Nd2O3, Dy2O3, and Yb2O3 as sintering additives, 3. Sialon ceramics with elongated alpha-sialon grains. The experimental resules showed that as to TiB(p), MoSi2(p), SiC(p), and SiC(w) second-phase reinforced Sialon materials, the toughening effect is mainly controlled by the bonding between matrix and second-phase and the critical size of second-phase particles. In Nd2O3-, Dy2O3-, and Yb2O3-added Sialon ceramics, Nd2O3 is a kind of effective sintering additive and Nd-Sialon possesses the highest K-1c, value (7.0 MPa.m(1/2)) due to the elongated beta-Sialon grains developed by heat treatment in order to induce in-situ self-toughening mechanism. Yb2O3 is not only an effective sintering additive, but also a useful alpha-Sialon stabilizer, so Yb-Sialon is hard, with a highest Vickers hardness H-v10 of 18.0 GPa, because of the existing of equiaxed alpha-Sialon grains in the samples. The action of Dy2O3 is between Nd2O3 and Yb2O3. The growth mechanism of elongated alpha-sialon grains is declared to be the heterogeneous nucleation and anisotropic growth.