Oxidation resistance of AlN–(TiB2–TiSi2) ceramics in air up to 1450 °C

With the aid of DTA, TG, XRD, SEM and EPMA methods the kinetics and mechanism of oxidation of both composite powders and monolithic ceramics of AlN–(TiB2–TiSi2) system with different content of components were studied in the air up to 1450 °C under isothermal and non-isothermal conditions. It was established that the oxidation isotherms of monolithic ceramics follow the parabolic and paralinear rate law. According to the kinetic data and results of investigation of composition, morphology and structure of oxide films that are formed at different temperatures, the AlN–based ceramics containing up to 30% (TiB2–TiSi2) solid solutions are the corrosion-resistant and have the high adhesion of oxide layer in relation to substrate material. The activation energies of oxidation calculated for ceramics with 10% (TiB2–TiSi2) are: E1 =180 kJ/mol for the temperature range up to 1300 °C and E2=630 kJ/mol at 1350–1450 °C. The change of activation energy value is associated with the change of oxide layer composition: at the oxidation till 1300 °C the oxides of individual elements are, mainly, formed on the samples while above 1350 °C the formation of very dense surface film containing β-tialite Al2TiO5 takes place.