Effects of α- and β-Ti phases as unreinforced or TiC-reinforced substrates on plasma electrolytic oxidation coatings for biomedical use

Abstract

This study addresses the critical need for advanced materials in bone implant applications, with a particular focus on biofunctional surfaces that exhibit enhanced wear resistance. Titanium (Ti) and its alloys offer favorable mechanical and anti-corrosive properties but are prone to degradation under frictional conditions, such as those in synovial joints. Ti-based matrix composites (TMCs), including α-Ti or β-Ti-alloy matrices reinforced with titanium carbide (TiC) particles, have emerged as potential wear-resistant biomaterials. The present investigation aims to further enhance the biological and tribological performance of TMCs through surface modification. The effects of substrate composition on the surface properties of coatings formed by Plasma Electrolytic Oxidation (PEO) were assessed using unreinforced α-Ti and β-alloy substrates, as well as their TiC-reinforced composites (α-TMC and β-TMC). The α-to-β phase transition significantly altered PEO coatings, reducing crystallinity (∼35 % to ∼5 %) and shifting the anatase-to-rutile ratio to 1:1. All PEO coatings formed porous oxide layers exceeding 5 μm in thickness, with β-type substrates yielding thicker, rougher coatings and finer porosity (>60 % submicron pores), favorable for biological integration. Surface wettability decreased following TiC addition and PEO treatment, while the surface free energy of β-TMC increased from 41.4 ± 4.4 to 54.5 ± 4.6 mJ/m2 after PEO. Overall, PEO treatment improved wear resistance. Notably, the TiC-reinforced substrate maintained higher coating integrity than the unreinforced β-alloy, showing minimal wear damage and a prolonged low-friction regime (COF ∼0.1 for >750 s) due to the “pillar effect” of TiC. These findings highlight β-TMC as a promising substrate for multifunctional bioactive coatings, enhancing durability and performance in biomedical applications.