The investigation of high-temperature oxidation takes many forms. Usually one is interested in the oxidation kinetics. Additionally, one is also interested in the nature of the oxidation process, i.e., the oxidation mechanism. Figure 1.1 is a simple schematic of the cross-section of an oxide formed on the surface of a metal or alloy. Mechanistic studies generally require careful examination of the reaction products formed with regard to their composition and morphology and often require examination of the metal or alloy substrate as well. Subsequent sections of this chapter will deal with the common techniques for measuring oxidation kinetics and examining reaction-product morphologies.

In measuring the kinetics of degradation and characterizing the corresponding microstructures questions arise as to the conditions to be used. Test conditions should be the same as the application under consideration. Unfortunately, the application conditions are often not precisely known and, even when known, can be extremely difficult to establish as a controlled test. Moreover, true simulation testing is usually impractical because the desired performance period is generally much longer than the length of time for which laboratory testing is feasible. The answer to this is accelerated, simulation testing.

Accelerated, simulation testing requires knowledge of microstructure and morphological changes. All materials used in engineering applications exhibit a microstructural evolution, beginning during fabrication and ending upon termination of their useful lives.