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

TLDR

Anodization of titanium and its alloys is an important surface treatment for adhesion, yet it is less studied than for aluminium alloys. This study characterizes the morphology, structure, and physicochemical properties of anodic oxide films on Ti and Ti–6Al–4V in chromic acid, with or without hydrofluoric acid, focusing on nanoporous formation, film thickness, composition, and the influence of Cr(VI) and F species. The films were examined by HR‑SEM, RHEED, XPS, SIMS, NRA, and wetting‑angle measurements, and a growth‑and‑dissolution mechanism was proposed. Compact CA films are amorphous while CA/HF films are partially crystalline, with a TiO₂+Al₂O₃ composition (Ti/Al ≈5), fluorine incorporated in the porous films, and trace vanadium present. © 1999 John Wiley & Sons, Ltd.

Abstract

Anodization of titanium and its alloys is an important surface treatment, especially for adhesion applications, but is not as well studied as for aluminium alloys. This paper deals with the morphological, structural and physicochemical characterization of anodic oxide films grown on titanium and Ti–6Al–4V (TA6V) in chromic acid solution without (CA) or with (CA/HF) hydrofluoric acid addition. Several investigations methods are used: high-resolution scanning electron microscopy (HR-SEM), reflection high-energy electron diffraction (RHEED), x-ray photoelectron spectroscopy (XPS), secondary ion mass 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 are amorphous and the porous films grown in the CA/HF solution are partially crystalline. The thickness and morphology of the films are described and discussed 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 ∽5), with incorporation of fluorine from the solution in the porous films and of small quantities of vanadium 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 © 1999 John Wiley & Sons, Ltd.