High-temperature (to 1670°C) air oxidation of AlN–Si3N4 and AlN–Si3N4–(Ni–Cr–Al) ceramic materials

The kinetics and mechanism of high-temperature air oxidation of powders and compact materials with different compositions in the AlN–Si3N4 and AlN–Si3N4–(Ni–Cr–Al) systems are studied using nonisothermal (up to 1500°C) and isothermal (1350 and 1670°C) thermogravimetry, DTA, XRD, petrography, and EMPA. During heating, Al4O4–xNx and Si2N2O oxynitrides, α-Al2O3 and α-SiO2 (crystobalite) oxides, and mullite-based Al2O3 ∙ SiO2 solid solution of the boundary composition form during the first oxidation stage, and 3Al2O3 ∙ 2SiO2 mullite forms at higher temperatures (>1350°C) in the upper scale layer and aluminum-nickel chromite spinel in the intermediate (barrier) scale layer. The AlN–Si3N4 and AlN–Si3N4–(Ni–Cr–Al) ceramics may be regarded as hightemperature composites (HTCs) owing to their high corrosion resistance.