Effect of relative humidity and temperature on the tribology of multilayer micro/nanocrystalline CVD diamond coatings

•The tribological behaviour of 10 layered micro/nanocrystalline diamond is studied•Delamination load triples from 40 N at 10%RH to 120 N at 90%RH•Very low wear coefficients of the plates were achieved via 3D optical profilometry•High temperature and low relative humidity have the same effects: low critical loads

The tribological behavior of tenfold micro/nanocrystalline CVD diamond multilayers is here investigated in self-mated configuration using ball-on-plate reciprocating wear testing. The effects of relative humidity (RH) and temperature (T) on friction and wear coefficients are assessed. The strongest effect of humidity was found on the value of the critical load (no delamination) that triples from 40 N at 10%RH to 120 N at 90%RH. Evaluation of the wear coefficients of the plates was only possible with the use of 3D optical profilometry. A valley-shaped evolution is observed for the wear coefficient of the plates, within the 10% to 90% RH range, with a minimum of about 1.7x10-7 mm3N-1.m-1, indicative of a mild wear regime, whereas the balls have lower values in the very mild wear regime of k ~ 10-8 mm3N-1.m-1. The clearest difference between the RH and temperature experiments is observed for the critical loads, limited to the range 40-55 N at 50-100°C, while at room temperature a value of 120 N was reached. However, the critical loads at high temperature are similar to those attained under dry conditions (≤ 25% RH) highlighting the absence of water as the load bearing medium.

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