Friction mechanism of DLC/MAO wear-resistant coatings with porous surface texture constructed in-situ by micro-arc oxidation

A porous textured DLC/MAO multilayer coating was constructed in-situ on Al alloy by depositing a diamond-like carbon (DLC) film onto a micro-arc oxidation (MAO) layer. The morphology, composition and tribological properties were investigated. The wear mechanism of the coating and the effect of load on wear were studied in detail under dry and oil-lubricated conditions. The results showed that DLC/MAO coating had excellent load-bearing capacity and wear resistance. The porous texture was generated in-situ on the aluminum alloy substrate by micro-arc oxidation technology, which played a mechanical interlocking effect in making the multi-layer coating tightly bonded. It can also capture wear debris to reduce abrasive wear under dry conditions while storing lubricating oil to supplement the lubricating film under oil-lubrication. DLC top film optimized the frictional resistance induced by the porous texture through graphitization and low-shear transfer film formation, reducing up to 70.7 % and 54.9 % in friction coefficient and wear track width under dry conditions. Under oil lubrication, the solid-liquid synergy between the graphitized layer and the liquid lubricating film can reduce the friction coefficient and wear track width by up to 20.9 % and 52.1 %. Hence, the combination of DLC top film and MAO tie layer realizes excellent anti-friction/wear and durability.