Abstract
Si3N4-Si2N2O-MN (M=B, Ti) composite ceramics were hot-pressed (HP) by using following reactions of 2B2O3 + Si3N4 = 4BN + 3SiO2 (i), 3TiO2 + Si3N4 = 3TiN + 3SiO2 + 1/2 N2 (i)', Si3N4+ SiO2 = 2Si2N2O (ii). Reactions during sintering were followed by XRD and sintered composites were characterized by XRD, SEM, TEM, four-point bending test and Vickers indentation method. XRD results and TEM observations showed that h-BN and TiN were formed at about 1200°C by the reaction of (i) and (i)'. The Si2N2O phase formed by reaction (ii) was found above 1800°C. Si3N4-Si2N2O-BN composite consisted of Si2N2O grains of 2-10 micro m in size with Si3N4 and h-BN grains of about 0.5 micro m in size. Strength of Si3N4-Si2N2O-BN composite was lower than that of Si2N2O ceramics but hardness and toughness were comparable to Si2N2O. Si3N4-Si2N2O-TiN composites also consisted of 2-10 micro m Si2N2O grains with small TiN about 0.5 micro m. Hardness and strength of Si3N4-Si2N2O-TiN composites were comparable to those of Si2N2O ceramics but toughness was greater than Si2N2O.
