Abstract
The long term oxidation resistance of most high temperature alloys depends on the ability to form protective alumina or chromia surface scales during service. Scale growth and scale rehealing after spalling leads to depletion of the scale forming element, aluminium or chromium, in the bulk alloy. If the concentration of this element decreases below a critical level, oxidation of the base elements, e.g. iron, nickel, or cobalt, occurs leading to catastrophic oxidation and destruction of the metallic component. Using iron based, alumina forming, oxide dispersion strengthened alloys as an example, a model is presented which allows the calculation of the time at which the catastrophic breakaway oxidation for a given component occurs. The calculated data are presented as oxidation diagrams in which the time to breakaway is plotted as a function of component wall thickness. Experimental data for the oxidation of the oxide dispersion strengthened alloys MA 956, PM 2000 and ODM 751 in air in the temperature range 1200–1400°C showed excellent agreement with the calculated oxidation diagrams.
MST/1839
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