Improving tribological performance of metallic coatings: A synergy of gradient structure and solid lubricant modification

Abstract

Metallic coatings are essential in providing anti-friction and wear-resistant protection to soft metals. However, they often encounter challenges in offering sufficient protection under demanding friction and wear conditions. In this study, by combining a gradient structure with solid lubricant modification, we fabricated gradient-structured (GS) Ni/graphite composite coatings through electrodeposition, showcasing superior tribological properties. Experimental results indicate that the GS Ni/graphite coating, when rubbed against WC-5%Co alloy, exhibits a coefficient of friction (COF) of 0.33 and a wear rate of 1.14 × 10−5 mm3/N·m, marking reductions of 47 % and 93 % respectively compared to the softer Cu alloy substrate. Comprehensive stress field evaluations and subsurface microstructural analyses attribute this enhanced tribological performance to the effective accommodation of plastic deformation within the subsurface layer by the gradient structure, coupled with the lubricating function of graphite. The synergy of the gradient structure and graphite presence contributes to preventing cracking and promoting a more resilient subsurface layer, resulting in decreased COF and improved wear resistance. This study not only highlights the notable tribological advancements attainable with GS Ni/graphite composite coatings but also introduces an advanced approach for developing novel GS metal/solid lubricant coatings with enhanced friction and wear properties.