The long-term oxidation behaviour of ferritic ODS alloys at 1100-1200°C in air and nitrogen-2% oxygen

The long-term isothermal oxidation behaviour of two ferritic ODS alloys (MA 956 and ODM 751) has been examined in air and in a flowing mixture of 2% oxygen in nitrogen at 1100-1200 degrees C for exposure times up to 8760 h. The oxidation rate of MA 956 was found to be significantly faster than that of ODM 751. The alumina scale formed on MA 956 was essentially equiaxed containing irregularly-shaped titanium-rich oxide particles whereas the oxide formed on ODM 751 was distinctly columnar and contained elongated yttrium-rich oxide particles. The scale on ODM 751 was found to be more resistant to spalling than that formed on MA 956. The faster oxidation rate and spalling of the alumina scale resulted in severe aluminium depletion in MA 956, which showed breakaway oxidation after 4900 h exposure at 1200 degrees C. (C) 1999 Elsevier Science Ltd. All rights reserved.