OXIDATION-INDUCED LIFETIME LIMITS OF THIN-WALLED, IRON-BASED, ALUMINAFORMING, OXIDE DISPERSION-STRENGTHENED ALLOY COMPONENTS

The long term oxidation resistance of most high temperature alloys dep ends on the ability to form protective alumina or chromia surface scal es during service. Scale growth and scale rehealing after spalling lea ds to depletion of the scale forming element, aluminium or chromium, i n 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 disp ersion strengthened alloys as an example, a model is presented which a llows the calculation of the time at which the catastrophic breakaway oxidation for a given component occurs. The calculated data are presen ted as oxidation diagrams in which the time to breakaway is plotted as a function of component wall thickness. Experimental data for the oxi dation of the oxide dispersion strengthened alloys MA 956, PM 2000 and ODM 751 in air in the temperature range 1200-1400-degrees-C showed ex cellent agreement with the calculated oxidation diagrams.