High-temperature oxidation behavior and mechanism of Si3N4/Si3N4w/TiN nanocomposites ceramic cutting tool materials

High-temperature oxidation behaviors were observed through the SEM, TEM and XRD observation. Only a few intergranular TiN grains are oxidized into TiO2 oxidation layers at 850 deg C, owning to intragranular structure of nanocomposites, and the thickness of oxidation layer without porosity is very thinner. At 1150 deg C, TiN grains and Si3N4 matrix grains are, respectively oxidized into TiO2 and SiO2 phase. However, the oxidation of intragranular TiN grains lags behind that of intergranular TiN and Si3N4 matrix grains because of the shielding action of Si3N4 matrix grains. With the increasing of oxidation duration at 1150 deg C, many cracks and pores were found in the oxidation layer. Based on the characteristics of microstructure and oxidation surface layer, the oxidation mechanism was proposed to describe the oxidation process of Si3N4/Si3N4w/TiN nanocomposites ceramic cutting tool materials.