OXIDATION OF IRON-ALUMINUM ALLOYS IN THE TEMPERATURE RANGE 500-900C.

The Oxidation of 1, 3, 5 weight percent aluminum-iron alloys in oxygen has been investigated at one atmospheric pressure over the temperature range 500 - 900C. The effect of temperature and alloy composition on the oxidation rate was determined by the gravimetric method. The scales formed on the alloy surfaces were examined using the technique of metallography, electron diffraction and electron microprobe analyses. The rate of oxidation decreased with increasing aluminum content and decreasing temperature. The oxidation followed approximately the parabolic rate law at the initial period of reaction. Microscopic examination of the oxidized specimens revealed the existence of two and three layers after oxidation at 500 and 600C, respectively. The inner layer contained a higher aluminum content. The oxidation at 700 - 900C gave a non-adherent outer layer in grey color. In areas where the oxide had spalled off, an adherent oxide layer was exposed. Small nodules with whiskers were observed at randomly distributed positions. Electron diffraction analysis of the surface of the 5 percent A1-Fe alloy indicated that the oxidation products consisted of a mixture of oxides. (Author)