Study of the relationship between the crystal structure and micro-nano morphology of anodized stainless steels

In this work, we found that stainless steels with different crystal structures generated two new surface micro-nano morphologies after anodization. The surface morphologies were observed by field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM). Element identification and quantitative analysis of each element were carried out using energy dispersive X-ray spectroscopy (EDS). Anodized stainless steel with a face-centered cubic crystal structure (SS-fcc) exhibits 45 degrees grooves along the crystal edges while stainless steel with a body-centered cubic structure (SS-bcc) has wedges protruding out of the anodized surface. The crystal structures and the percentage of crystal planes of SS-fcc and SS-bcc were characterized using X-ray diffraction (XRD) before and after anodization. It was observed that different crystal facets of SS-fcc and SS-bcc disappear at different rates during anodization. This explains the different micro-nano morphologies observed during the anodization process. It is concluded that different crystal planes have different anodization properties and the degree of disappearance of the crystal plane is consistent with its energy order.