Nodular defects aggravated tribocorrosion failure mechanism in Cr/GLC multilayer coatings for marine applications

Amorphous carbon coatings by various physical vapor deposition (PVD) have been widely attempted for enhancing both anti-wear and corrosion resistance of bulk materials used in harsh marine environments. However, PVD coatings are apt to be worn due to the existence of growth defects mostly like macro-size nodular particles. In this work, we deliberately fabricated the SiO2 nanoparticles with a size of 200 nm as nodular defects in Cr and graphite-like carbon (Cr/GLC) multilayer coatings, and the dependence of tribocorrosion behavior of coating on the nodular defects was focused by the comprehensively tribological and electrochemical tests. The results showed that introducing SiO2 nodular particles could not degrade the mechanical properties of Cr/GLC coating, but significantly accelerated both the abrasive wear in early sliding-stage under dry friction and the corrosive failure in chloride solution. Particularly, once the tribocorrosion tests in 3.5 wt.% NaCl solution were conducted for the Cr/GLC coating with nodular defects, the distinct ploughing damage originated from abrasive wear promoted the localized spallation of coatings, which thereafter enabled the easy water wedging along spallation for the substantial catastrophe of coatings. The present observations could evident the importance to fabricate the defect-free protective coatings required for harsh tribocorrosion applications.