(Invited) Growth of Anodic Nanotubular Oxides: The Influence of Substrate

Abstract

In the present work, we examined the growth of nanotubular oxide layers by anodization in fluoride containing electrolytes, focusing on the influence of substrate. The properties of substrate such as defect density and the size of microstructure were varied. The defect density and the size of microstructure were controlled by cold work and heat-treatment. Cold work increased the defect density of Ti substrate whereas heat-treatment decreased the defect density within Ti. These substrates were subjected to the anodization in ethylene glycol containing ammonium fluoride and water. Cross-sectional observations revealed that the defect density affected the growth of nanotubular oxide layers on Ti substrate, that is, on Ti substrate with increased defect density by cold work, the thickness of nanotubular oxide layer increased while on Ti substrate with decreased defect by heat treatment, the thickness decreased. The size of microstructure also exhibited strong influence on the growth of nanotubular oxide layer. For this purpose, lamellar Ti-41at.%Al alloys consisting of Ti3Al and TiAl were prepared. The width of the lamellas was controlled by heat treatment. On the alloy with wider lamellas, nanotubular oxide layers were formed on each phase. On the other hand, selective growth of pore was achieved when the width of lamella was below critical size. Therefore, these results indicate that the properties of substrate strongly affect the growth of anodic nanotubular oxide layers.