Fabrication and properties of Si(sub 3)N(sub 4) with rare earth apatite grain boundary phases

摘要

The rare earth-oxide and nitride apatites were examined as grain boundary phases in silicon nitride to assess their potential for developing high toughness materials using gas-pressure-sintering. Densification was dependent on the quantity of additives used with high densities achieved at equivalent oxygen contents of (approximately)8%. Fracture toughnesses (K(sub Ic)) up to 8--10 MPA(radical)m were obtained for some compositions. Ambient temperature flexural strengths were in the range of 400--720 MPa; however, the strengths at elevated temperatures (1200(degrees)C) were reduced from these values.