Micro/nanotribology of ultra-thin hard amorphous carbon coatings using atomic force/friction force microscopy

Abstract

Microscale scratch and wear resistance tests using an atomic force microscope have been conducted on ultra-thin hard amorphous carbon coatings, often called diamond-like carbon (DLC) coatings, deposited using filtered cathodic arc (FCA), direct ion beam (IB), electron cyclotron resonance plasma chemical vapour deposition (ECR-CVD) and sputter (SP) deposition processes. Coating thicknesses of 20, 10, 5 nm and, for the first time, 3.5 nm coatings, have been investigated. The objectives of the study were to identify the thinnest coating that exhibits good wear-resistance, to identify deposition processes that produced superior coatings for wear-resistance and to understand failure mechanisms of such ultra-thin coatings during wear. It was found that, in general, the thicker coatings exhibited better scratch/wear performance than thinner coatings due to their better load-carrying capacity as compared to the thinner coatings. At 20 nm, ECR-CVD and FCA coatings showed the best wear resistance. At 10 nm, ECR-CVD was the best, while IB coating showed the best wear resistance at 5 nm. Five nanometer coatings showed reasonable wear resistance, while 3.5 nm coatings showed extremely low load-carrying capacity, poor wear resistance and evidence of early coating delamination. Although IB and ECR-CVD 3.5 nm coatings showed some amount of wear resistance at low loads, it appears that the 3.5 nm coatings studied are infeasible for wear-resistant applications as of now.