Surface damage mitigation of Ti6Al4V alloy via thermal oxidation for oil and gas exploitation application: characterization of the microstructure and evaluation of the surface performance

Abstract

Because of its disadvantages of low surface hardness values, a high coefficient of friction and poor wear resistance, Ti6Al4V alloy is seldom used in tribological-related engineering components. To improve the surface performance of Ti6Al4V alloy used as petroleum tubes for oil and gas exploitation applications, a thermal oxidation (TO) process was applied to fabricate a TO layer on the Ti6Al4V substrate at 700 °C for 30 h. A microstructural characterization of the produced TO layer was systematically performed. Comparative estimations of the electrochemical corrosion, erosive-wear and corrosive-wear behaviors on the TO layers and Ti6Al4V alloys were conducted in CO₂-saturated simulated oilfield brine. The results showed that the obtained TO layer was mainly composed of rutile phase TiO₂ and minor anatase phase TiO₂. The continuous and compact TO layer reached a total thickness of about 20 μm. The TO layer contained an external oxide-layer and an internal O-diffusion layer. The concentration of O had a gradient descent along the thickness of the TO layer. The TO layer showed enhanced hardness and good bonding strength. Compared to the Ti6Al4V alloy substrates, the TO layers revealed superior surface performance in the electrochemical corrosion, erosive-wear and corrosive-wear tests. Excellent chemical stability, mechanical isolation action, high hardness and bonding strength contributed to the promising surface performance of the TO layer. TO treatment makes it possible to create a working surface on the Ti6Al4V alloy with enhanced surface hardness and wear resistance.