Synthesis, thermodynamic stability and diffusion mechanism of Al 5Fe2-based coatings
Aluminide coating of steels enables more efficient power generation through higher operating temperatures. Low-temperature (T < 660 C) pack cementation aluminide coatings form an Al5Fe2 phase which allows for the development of a large Al flux, but the mechanism is not clear. The coating structures and resultant oxides were examined in both austenitic and ferritic steels at 1,000 and 800 C to evaluate the high temperature oxidation behavior in air. To understand the relatively fast Al diffusion, the stability of the Al5Fe2 phase and the defect structure have been examined by a cluster expansion method with density functional theory calculations. The Al5Fe2 phase has a low site occupancy and a high vacancy content that promotes rapid kinetics. The high vacancy concentration in the Al5Fe2 phase can be traced to the interaction between Al and vacancies along the  chains. The analysis offers useful guidance to enable an effective control of low temperature aluminizing.
Al Fe 5 2, Aluminide coatings, Density functional theory, Pack defect structure
Sakidja, R., J. H. Perepezko, and P. Calhoun. "Synthesis, thermodynamic stability and diffusion mechanism of Al 5 Fe 2-based coatings." Oxidation of metals 81, no. 1 (2014): 167-177.
Oxidation of Metals