Electrochemical corrosion and tribological properties of CrMoCN coatings sliding against Al2O3 balls in artificial seawater

Abstract

Due to low density and high specific strength, titanium alloys have been widely used for marine applications. However, the severe wear and corrosion of titanium alloy components is still a problem. To alleviate this problem, protective coatings are applied. In here, the influence of Mo content on the protective performance of CrMoCN coating for Ti-6Al-4V substrate has been investigated. The short- and long-term corrosion resistances of coating in artificial seawater are studied using an electrochemical workstation with three-electrode configuration. The tribological behaviors of CrMoCN coating sliding against Al2O3 ball are evaluated using a ball-on-disk tribo-meter. The results reveal that the CrMoCN coated samples have higher wear- and corrosion-resistances than the bare substrate. The CrMoCN coating with 8.1 at.% Mo displays the highest values of OCP (0.22 V), Rct ((8.639 ± 0.270) × 107 Ω·cm2) and Rp ((3.04 ± 0.24) × 106 Ω·cm2). However, their protective performances are degraded in the long-term, and then the Rp of CrMoCN-2.5 coating continuously decreases from (5.99 ± 0.47) × 105 Ω·cm2 at 7 days to (0.13 ± 0.01) × 105 Ω·cm2 at 35 days. With an increase in the Mo content, the friction coefficient of CrMoCN coating/Al2O3 tribopair decreases from 0.36 to 0.31 while the coating wear rate increases from 4.65 × 10−7 mm3/Nm to 1.01 × 10−6 mm3/Nm.