Structure and physicochemistry of anodic oxide films on titanium and TA6V alloy

Anodization of titanium and its alloys is an important surface treatment, e specially for adhesion applications, but is not as well studied as for alum inium alloys. This paper deals with the morphological, structural and physi cochemical characterization of anodic oxide films grown on titanium and Ti- 6Al-4V (TA6V) in chromic acid solution without (CA) or with (CA/HF) hydrofl uoric acid addition, Several investigations methods are used: high-resoluti on scanning electron microscopy (HR-SEM), reflection high-energy electron d iffraction (RHEED), x-ray photoelectron spectroscopy (XPS), secondary ion m ass spectrometry (SIMS), nuclear reaction analysis (NRA) and wetting angle measurements. The occurrence and morphology of the nanoporous structure for CA/HF anodization are described. The compact films grown in CA solution ar e amorphous and the porous films grown in the CA/HF solution are partially crystalline. The thickness and morphology of the films are described and di scussed as a function of the anodizing conditions and of the composition of the underlying substrate. The composition of the film appears to be TiO2 Al2O3 (with Ti/Al atomic ratio similar to 5), with incorporation of fluori ne from the solution in the porous films and of small quantities of vanadiu m in the films that are grown. The specific role played by the Cr(VI) and F species on the film growth-and-dissolution formation process is discussed and a growth mechanism is proposed, Copyright (C) 1999 John Whey & Sons, Lt d.