Wear and Friction Characteristics of Ti-6Al-4VT Alloy Treated by Plasma Electrolytic Oxidation (PEO) Process for Aerospace Applications

Titanium alloy type Ti-6Al-4V alloy is widely considered in aerospace applications for replacement of steels due to its low density, mechanical strength, good corrosion resistance and good thermal conductivity. However, it is highly susceptible to fretting and adhesive wear in addition to its very unstable and high friction coefficient in a tribological environment. A number of surface technologies including anodizing and thermal oxidation are not considered suitable for applications involving contact pressures and wear, primarily due to an insufficient oxide thickness, poor adhesion of the oxide layer and insufficient surface hardness.

This paper presents the tribological characteristics of Ti-6Al-4V alloy treated using the Keronite plasma electrolytic oxidation (PEO) process. Microstructure and crystallinity of the coating has been examined and the coating characteristics such as roughness, porosity, hardness, thickness uniformity and phase composition have been investigated. In addition, this study looked into the effect of post-coating polishing and impregnation with MoS₂ on the wear and friction responses.

Block (steel)-on-ring (coated titanium) sliding wear testing per ASTM D 2714 and Taber abrasion wear testing per ASTM D 4060 have been performed. The wear mechanism in relation to the coating morphology, composition and structure has been examined using scanning electron microscopy (SEM), Auger electron spectroscopy and energy dispersive X-ray (EDX) analysis. Performance has been compared against an uncoated Ti-6Al-4V alloy and other common wear surface treatments. The results to improve the tribological performance of Ti-6Al-4V alloy for use in aerospace landing gear applications are discussed.