Processing and characterization of SiB_0.5C_1.5N_0.5 produced by mechanical alloying and subsequent spark plasma sintering

SiB_0.5C_1.5N_0.5 nanopowders were synthesized by mechanical alloying method, and a predominantly amorphous with a small volume fraction of nanocrystalline phase was formed in the powders. The results showed that the crystallites were SiC, and the polytype of SiC were 3C and 6H. SiB_0.5C_1.5N_0.5 powders were consolidated by spark plasma sintering (SPS) technique at 1800 °C under different sintering pressure. The grain boundaries of SiC and BCN phase could not be clearly distinguished for the ceramics sintered under 25 MPa. When the pressure increased to 40 MPa, SiC phase almost completely crystallized, and its grain size was less than 1 μm. BCN phase were mainly distributed at boundary of SiC grain. Some amorphous structures were found in the sintered ceramics. Relative densities of the ceramics increased from 76.6% to 92.4%, and mechanical property values increased two or three times with the increase of sintering pressure. For the ceramics sintered under a pressure of 40 MPa, flexural strength, fracture toughness, elastic modulus and Vickers' hardness attained to 311.5 MPa, 3.45 MPa m^1/2, 133.0 GPa and 3.68 GPa, respectively. The mass of the SiBCN ceramics lose by several percent below 930 °C in air, and then keep unchanged above 1100 °C.