Diffusion and plasma oxidation mechanism of Fe–Al coatings

Al coatings were deposited using a pure Al target directly onto pure iron substrates at different temperatures by double glow discharge technique. Then, the Fe–Al coatings were plasma oxidised at 580°C. The results indicated that the aluminide layer was nanocrystalline with many crystal defects after the aluminising process. The oxidation kinetics showed a two-stage behaviour. The energetic O ions with higher driving force diffused into the coatings at the beginning of the oxidation. Then, O ions diffused via short circuit diffusion caused by the existence of large amounts of grain boundaries and crystal defects. After oxidation, α-Al₂O₃, γ-Al₂O₃ and Fe₂O₃ phases were detected. Large amount of voids filled with oxide ions were formed at the outermost aluminide layer owing to the different intrinsic diffusivities of Fe and Al.