Metallurgical aspects on the formation of self-organized anodic oxide nanotube layers

The present work reports how metallurgical factors such as grain size and chemical composition of substrate affect the current behavior during anodization and the morphology of resulting formed oxide layers. The grain size of pure Ti sheet is controlled by the accumulative roll-bonding (ARB) process. Tubular oxide layers are formed on the ARB-processed Ti sheets with different grain sizes, but grain size does not affect the length, diameter of tubes and the degree of tube arrangement. The effect of chemical composition is examined using Ti–Zr alloys (Ti–20Zr, Ti–50Zr, Ti–80Zr) that can consist of a single phase, meaning that homogeneous tube formation can be achieved. With increasing Zr content in the alloys, tube diameter decreases while tube length increases. For the Ti–50Zr and Ti–80Zr, self-organization is achieved on two size scales, that is, nanotube arrays with two distinct diameters are observed. TEM observation revealed that anodic oxide layers are in crystalline state only in the case of pure Zr.