The specifics of high-temperature air corrosion of composite cermet materials of the system (AlN-Al2O3)-(Ni-Cr-Al) are considered. The oxidation kinetics is studied by thermogravimetric (TG) and differential thermal analysis (DTA) methods on compact samples and on the respective composite powders under nonisothermal (up to 1500°C) and isothermal (at 1350°C) conditions. It is demonstrated that high-temperature oxidation of powders and pore-free hot-pressed samples occurs in two stages. In the first stage, nickel and chrome oxides and aluminum oxynitride are formed at lower temperatures on the sample surface; in the second stage, the oxides react and form solid solutions Al2O3-Cr2O3 and spinel Ni(Cr, Al)2O4. Both compact and powder composites with 20% metallic binder are oxidized at a higher rate than composites containing 40% binder. In all cases the corrosion of the material is accompanied by the formation of a two-layer oxide film, The external part of the film contains the solid solution Al2O3-Cr2O3 and the interior part consists of nickel alumochromite spinel Ni(Cr, Al)2O4 and Al2O3 oxide. Oxidation of composite materials based on AlN-Al2O3 with a (Ni-Cr-Al) binder is characterized by an exceptionally low weight increment.
Refractories and Industrial Ceramics – Springer Journals
Published: Aug 13, 2007
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