Development of calcium stabilized nitrogen rich α-sialon ceramics along the Si₃N₄:1/2Ca₃N₂:3AlN line using spark plasma sintering

Calcium stabilized nitrogen rich sialon ceramics having a general formula of Ca_xSi_12-2xAl_2xN₁₆ with x value (x is the solubility of cation Ca in α-sialon structure) in the range of 0.2–2.2 for compositions lying along the Si₃N₄:1/2Ca₃N₂:3AlN line were synthesized using nano/submicron size starting powder precursors and spark plasma sintering (SPS) technique. The development of calcium stabilized nitrogen rich sialon ceramics at a significantly low sintering temperature of 1500 °C (typically reported a temperature of 1700 °C or greater) remains to be the highlight of the present study. The SPS processed sialons were characterized for their microstructure, phase and compositional analysis, and physical and mechanical properties. Furthermore, a correlation was developed between the lattice parameters and the content (x) of the alkaline metal cation in the α-sialon phase. Well-densified single-phase nitrogen rich α-sialon ceramics were achieved in the range of 0.53(3) ⩽ x ⩽ 1.27(3). A nitrogen rich α-sialon sample possessing a maximum hardness of 22.4 GPa and fracture toughness of 6.1 MPa·m^1/2 was developed.