In this study, amorphous hydrogenated carbon (a-C:H) and Si-doped diamond-like carbon (Si-DLC) films were prepared using microwave sheath voltage combination plasma (MVP) deposition. The thermal stability of the a-C:H and Si-DLC films were investigated by performing an annealing test (100-700°C) in ambient air. Furthermore, the in situ high-temperature tribological properties on the films were investigated by performing a sliding test against a Si3N4 ball at high temperatures (100, 200, and 300°C). Hardness measurements and a tribological test showed that Si-DLC has better thermal stability than a-C:H; however, Si-DLC has a higher friction coefficient and undergoes more wear than does a-C:H in the in situ high-temperature tribological test. Therefore, the failure of Si-DLC is due to adhesive wear, whereas that of a-C:H is due to abrasive wear.
A concept of wear monitoring of tribological coating has been proposed and extended to monitor the wear life of amorphous carbon (a-C) films. The wear sensing layer that is an epoxy resin coating containing luminescent ZnS:Cu powder (EP/ZnS:Cu) is located between a-C film and silicon wafer substrate. The tribological performances of the coating have been examined by a ball-on-disk friction test, as well as wear sensing capability by detecting luminescence from the wear track. As-prepared EP/ZnS:Cu layer coating exhibited a strong green luminescence when irradiated with a UV light at 365 nm. Subsequently, a-C films were deposited onto EP/ZnS:Cu layers to the thickness at which the luminescence could not be detected from those layers. It was found that a-C film with EP/ZnS:Cu underlayer rubbed against stainless steel ball at a normal load of 0.77 N for 50 m showed the coefficient of friction (μ) at 0.35 accompanying with the wear of stainless steel ball instead of the coating. This indicated that the coating was durable to a stainless steel ball. As a result, the luminescence from the wear track of the coating was undetected. In contrast, a-C film with EP/ZnS:Cu underlayer rubbed against alumina ball showed the lower μ = 0.15 accompanying with the removal or wear of a-C film. This has led to the luminescence from the wear track, which corresponded to the luminescence from EP/ZnS:Cu underlayer. The results suggested the feasibility to monitor the wear life of a-C film through luminescence from epoxy resin underlayer containing a phosphor powder.