The long-term oxidation behaviour of ferritic ODS alloys at 1100-1200 degrees 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% o xygen in nitrogen at 1100-1200 degrees C for exposure times up to 8760 h. T he 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 con taining irregularly-shaped titanium-rich oxide particles whereas the oxide formed on ODM 751 was distinctly columnar and contained elongated yttrium-r ich 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 spallin g of the alumina scale resulted in severe aluminium depletion in MA 956, wh ich showed breakaway oxidation after 4900 h exposure at 1200 degrees C. (C) 1999 Elsevier Science Ltd. All rights reserved.