Friction and Delamination Properties of Self-Mating Diamond-Like Carbon Coatings in Water

Abstract

The friction and delamination properties of self-mating diamond-like carbon (DLC) coatings in water and ambient air were investigated using a ball-on-disk tribometer. An a-C:H-type DLC coating was deposited on SUJ2 bearing steel using plasma chemical vapor deposition. Delamination of DLC coatings occurred in water in relatively mild contact conditions, such as applying a low load and a high sliding speed. However, no delamination occurred under severe contact conditions. Furthermore, delamination never occurred under ambient air conditions. The process that prevents delamination occurring under ambient air conditions is clarified using a detailed analysis of SEM data. Micro-cracks were caused by Hertzian contact with droplets, which then propagated into large ruptures under water conditions; however, they disappeared and formed a smooth surface under ambient air conditions. This is because of the structural change to an sp2-rich surface. Enhancement of the structural change of DLC coating could suppress delamination in water.