Effect of sintering atmosphere on the grain growth and hardness of SiC/polysilazane ceramic composites

Silicon carbide (SiC) monoliths were synthesised using nano-size SiC powder mixed with/without polysilazane by hot pressing at 1750°C for 1 h under an applied pressure of 20 MPa in N2 or Ar atmosphere. The effects of polysilazane and sintering atmosphere on the microstructure and hardness of SiC were examined. The grain sizes of the SiC ceramics sintered in N2 atmosphere with and without the polysilazane were 161 and 605 nm, while the density for those samples were 96.5 and 98.1%, respectively. It was shown that Si2N2O was formed for the SiC/polysilazane composite and sintered in N2. In addition, the sample mixed with polysilazane followed by sintering in N2 atmosphere revealed a quite high hardness in spite of its relatively low density. It was suggested that Si2N2O phase played an important role for the inhibition of grain and subsequent high hardness.