Demonstration of Wear Monitoring of Amorphous Carbon Films with Epoxy Resin Underlayer Containing Phosphor

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.