Effects of the crystal orientation of aluminum substrates on the formation behavior of AlO(OH) films

The influence of the crystal orientation on the formation of films has been demonstrated in various systems. However, its effect on AlO(OH) films formed through the steam coating process remains unexplored. This study addresses this gap by investigating the formation behavior of AlO(OH) films produced through steam coating on pure aluminum single-crystal substrates with controlled surface crystal orientations. The surface morphology and thickness of the film were evaluated for substrates with different crystal orientations, such as (100), (110), and (111). The results revealed that the crystal orientation of the substrate does not influence the surface morphology of the film but affects the film thickness of the dense layer. Moreover, the film thickness of the dense layer increases linearly with the processing time. These results suggest that the growth of the dense layer is governed by reactions at the substrate and dense layer interface rather than diffusion. This research highlights the possibility of new surface treatments to deposit different types of film depending on requirements, such as thick films with excellent corrosion resistance or thin films with low dimensional tolerance.