XPS investigation of heat-treated MAO coatings on Ti–25Ta alloy
Pedro Akira Bazaglia Kuroda, Carlos Roberto Grandini, Conrado Ramos Moreira Afonso
Abstract
This study aimed to perform a comprehensive chemical and structural characterization of MAO coatings enriched with calcium, phosphorus, magnesium, and carbon, produced on the Ti-25Ta alloy and subsequently subjected to heat treatments at 600, 700, and 800 °C. A key challenge in MAO coatings on Ti-25Ta alloys is achieving and maintaining optimal chemical bonding, crystallinity, and structural stability after heat treatment, which are crucial for their mechanical and biological performance. High-resolution X-ray photoelectron spectroscopy (XPS) was employed to quantify the chemical composition and oxidation states of the coatings, providing detailed insights into the surface chemistry and phase evolution. The results demonstrated that the MAO coatings are highly sensitive to heat treatment, with significant modifications in phase composition and chemical states. Heat exposure led to partial reduction of TiO 2 , formation of sub-stoichiometric Ti 2 O 3 , and, at higher temperatures, the emergence of TiC and metallic Ti. In contrast, Ta 2 O 5 remained thermally stable, reflecting the exceptional oxidation resistance of tantalum. The heat treatments also induced partial degradation of surface carbonates (CaCO 3 and MgCO 3 ) and the elimination of hydroxyl groups (OH - ) due to condensation, while phosphate species remained largely intact. The study highlights the critical role of XPS in elucidating the detailed surface chemistry and phase transformations of MAO-treated Ti-25Ta coatings under thermal treatment conditions.