High temperature oxidation behaviour of FeAl intermetallics—oxide scales formed in ambient atmosphere

Abstract

Iron aluminides (Fe-Al) are intermetallic compounds that possess a number of advantages including low materials cost, conservation of Ni and Cr, relatively low densities, and good corrosion and oxidation resistances. The authors have studied the high temperature oxidation and sulfidation behaviors of Fe-Al, including isothermal and cyclic oxidation kinetics, scale structure and spallation tendency, and the reactive elements effects (REE) in an effort to use these materials in industries. This paper reports their results on the structures and formation mechanisms of the scales formed on Fe-Al during oxidation. The scales formed on alloys after exposure to high temperatures often have a complex structure and composition. It is known that when some alloys were oxidized in air at high temperatures, nitrides were formed underneath the oxide scale. It was reported that the oxidation of TiAl alloys in an ambient atmosphere led to the nitration of the base metal beneath the oxide scales. After a long exposure time a multilayered scale was formed which consisted of metal, Ti{sub 2}AlN, TiN, TiO{sub 2} and Al{sub 2}O{sub 3}. Cr was oxidized in air at 1,200 C, forming a Cr{sub 2}O{sub 3} scale with a layer of Cr{sub 2}N beneath the oxide. When binary Crmore » alloys containing Ti,Zr, or Nb were oxidized in air at 1,150 C, a layer or internally distributed Cr{sub 2}N formed beneath the oxide scales. However, the structures and formation mechanisms of these types of scales are not clear. The authors have also found that the scales formed on Fe-Al at 1,100 C in air have a complex structure containing nitrides. This paper reports the authors' studies on this subject.« less