Oxidation at high temperature involves the oxidation of reactive elements, formation of oxide scales and internal oxidation. A knowledge of the reaction kinetics and the nature of the surface scales formed during oxidation is important for evaluating the alloys for their use and degradation characteristics in high-temperature applications. The oxidation behavior of complex alloys (ferritic iron-base alloys: AISI 430. AISI 434, AISI 430 Si, AISI 430 Ti and AISI 430 Ti-Al, austenitic iron-base alloys: AISI 310, AISI 314, Fel5Cr26Ni (with and without manganese), nickel-base alloys: Ni20Cr, Ni20Cr + Si, Incoloy 800, Inconel 718 and Inconel X) has been studied in the range 1073-1273 K in air using surface analytical techniques : grazing incidence XRD, FTIR specular reflectance spectroscopy, XPS and SEM-EDS. The roles of various minor alloying additions; manganese, silicium, titanium, aluminum, vanadium and niobium are considered and correlated with the overall oxidation process An oxidation mechanism for each alloy is proposed.

The oxidation mechanism of most of the alloys is mainly controlled by the outward manganese and titanium diffusion and induces the formation of duplex scales. Titanium acts as a third element in AISI 430 Ti-Al and enables aluminum to diffuse to the surface from the bulk, resulting in development of a healing Al₂O₃ layer in spite of the low alloy aluminum concentration. Internal (mainly intergranular) oxidation is substantial for alloys containing Al, Ti and Si and can be correlated with the depth of chromium depletion.

Spalling of oxide scale may be correlated with the presence of S, Si and Mn and that of elements (V, Mo) forming oxides with a low melting point. The likelihood of breakaway oxidation is important when the chromium depletion has penetrated a considerable distance in the alloy.