Multi-step anodizing on Ti6Al4V components to improve tribomechanical performances

This work presents the production and characterization of a controlled electrochemical modification of titanium surfaces, consisting of a two-step anodic spark deposition (ASD) process and a barrel finishing. The treatment was performed on titanium alloy Ti6Al4V, as most representative titanium alloy used in mechanical and aeronautical applications, where improved adhesion and tribological performances are required. FIB/SEM microstructural observations, nanoindentation, scratch, fretting tests and wear and friction tests were carried out both on laboratory specimens (planar pellets, 1. in. diameter) and on Ti6Al4V bolts of different shapes and sizes, to investigate the effect of a three dimensional shape on the correct execution of the electrochemical treatment and on the coating's mechanical performance. The formation of a double layered coating was observed, with a slightly decreased surface hardness and stiffness compared to the metallic substrate and increased scratch and fretting wear resistances, thanks to an excellent adherence to the substrate, an optimal value of the hardness to modulus ratio (H/E) and a marked decrease of the friction coefficient. The proposed coating procedure could be therefore a suitable solution for those applications where low friction, wear resistance under low load sliding contact and corrosion resistance are required. © 2012 Elsevier B.V.