The effect of anodization temperature of nitinol alloy on the morphology of surface nanoporous layer

Fabrication of nanostructures through anodization is a promising process as the technique enables easy and low-cost surface modification of metallic substrates with a high degree of control on the resulted nanostructure morphology. In this work, NiTi alloy (nitinol) was anodized in an organic-based electrolyte containing water and Cl- ions under different anodization temperatures with the aim of investigating the effect of the electrolyte temperature on the morphology and geometry of the obtained nanopores (NPs). According to electron microscopy and statistical analyses, by increasing the anodization temperature, the thickness of the obtained NP layer and the number of formed NPs are decreased, whereas their mean diameter is increased. It is concluded that anodization at room temperature results in the highest obtainable thickness for the NP layer, whereas the samples anodized at 40°C show the highest uniformity in regard to the NP layer thickness and the total number of the formed NPs. Meanwhile, anodization at temperatures around and beyond 80°C results in total destruction of the NP layer. The variations are explained by the dependency of the electrolyte viscosity and thereby the dissolution rate of the anodically-grown oxide layer on the anodization temperature.