A kinetic model for iron aluminide coatings by low-pressure chemical vapor deposition Part I. Deposition kinetics

Kinetics of formation of iron aluminide diffusion coatings by chemical vapor deposition (CVD) on pure iron was studied in the temperature range 1173-1373 K. AlCl3 vapor, produced by the sublimation of anhydrous aluminum chloride, was used for transporting aluminum from an aluminum source (pure aluminum) in the CVD reactor to the substrate to produce the coating. The reactor pressure was maintained at 1.33±0.133 kPa. The first step in developing a theoretical model for the coating process is to establish the kinetics of the process. This was accomplished by monitoring the weight gain and thickness as a function of time and temperature. The growth followed a parabolic rate law with the rate constant (by weight gain) steadily increasing with substrate temperature from 0.0114 mg2 cm-4 s-1at 1198 K to 0.0836 mg2 cm-4 s-1 at 1348 K. The rate constants were 4.138x10-6 and 6.554x10-6 mm2 s-1 (by thickness) at substrate temperatures 1273 and 1323 K, respectively. The activation energy for the coating process was 211±8 kJ mol-1