Microcrack generation and its healing in the oxide scale formed on Fe-Cr alloys

Fe -base alloys containing 5, 10, and 20 wt. % Cr were oxidized in a stream of O₂ at 750 and 900°C up to 264 hr. A sulfur decoration method was applied to detect the cracks generated in the scale during oxidation. This method revealed frequent crack generation and its healing in the scale. In the case of low-Cr alloys, the cracks are filled up with newly formed Fe-rich oxide but may be regenerated during further oxidation. Cracks are generated in the scale on an Fe-20Cr alloy also, although this alloy is not so severely attacked because of rapid healing.