Nano- and microstructure of diamond-like carbon films modified by Ca–O incorporation

Abstract

In the present study, the nano- and microstructure of diamond-like carbon (DLC) coatings on Ti6Al4V substrates were changed by Ca–O incorporation. For the deposition of Ca–O-DLCs, a gaseous hydrocarbon precursor (e.g. methane) and CaO–H 2O vapour were decomposed together in plasma using a direct current discharge. The hardness, Young's modulus and relative elastic recovery of Ca–O-modified DLCs are reduced in comparison to unmodified DLC. However, the adherence of the Ca–O-DLCs is improved. With increasing relative partial pressure of the CaO–H 2O vapour during DLC coating deposition, the size of the sp 2-hybridised carbon islands, which were observed via high-resolution transmission electron microscopy, increased and the shape changed from oval islands to strips of several 10 nm. This finding is in good accordance with the results from Raman spectroscopy, which also pointed to an increase in the size and/or number of sp 2-hybridised crystalline carbon clusters in the amorphous carbon matrix. The DLCs have increased oxygen content due to the decomposition of CaO–H 2O vapour, in addition to hydrocarbon. As detected by IR and X-ray photoelectron spectroscopy, Ca is incorporated as carbonate into the DLC.