Amorphous hydrogenated carbon (a-C:H) films are widely used as protective solid lubricant coatings in tribo-mechanical applications such as car engines, magnetic storage disks, and biomedical implants. However, these films can exhibit low thermal stability and high residual stresses, and their frictional and wear properties can strongly deteriorate due to changes in the gaseous sliding environment [1]. In the literature, silicon oxide doped diamond-like carbon (SiOx-DLC) films, also called diamond-like nanocomposite (DLN), exhibit better thermal stability [2] and are less sensitive to the environment [3] than a-C:H films. A convincing model to explain the mechanisms responsible for the improved stability does not yet exist. This work aims to identify the origin of the unique macroscopic tribological properties of DLN films under different environments (ambient air, ultrahigh vacuum, oxygen gas, and hydrogen gas).Friction experiments were performed with two linear reciprocating pin-on-flat tribometers, one operating in ambient air but allowing gas blowing around the contact, and the other placed inside an ultrahigh vacuum (UHV) chamber allowing gas introduction up to 2 atmospheres and equipped with differential mass spectroscopy [4]. Ambient air tribometry tests using steel conterfaces provide evidence of the dependence of the interfacial shear strength on humidity, and tribotests carried out under UHV conditions indicated that the friction response is mainly controlled by the adhesive interactions between DLN film and the counterface.In this talk, we will address a key question: does the presence of reactive gases prevent the formation of adhesive junctions by surface passivation, or does it affect the way these junctions are released? A combination of morphological observations and surface analyses are used to help us answer this question. References :[1] J. Robertson � Diamond-like amorphous carbon �  Material science and engeneering 37, 129-281 (2002)[2] C. Jongwannasiri, X. Xianghui Li, S. Watanabe � Improvement of Thermal Stability and tribological performance of diamond-like carbon composite thin films �, Materials Sciences and Applications, 4, 630-636 (2013)[3] T. W. Scharf, J. A. Ohlhausen, D. R. Tallant, S. V. Prasad � Mechanisms of friction in diamondlike nanocomposite coatings � Journal of Applied Physics 101, 063521 (2013)[4] J. Tannous, M-I. De Barros Bouchet, Th. Le Mogne, P. Charles, J.M Martin : � Contribution of gas phase lubrication in understanding tribochemistry of organosulphur compounds � Tribology 1(2), 98�104 (2007)

Do silicon oxide doped DLC (SiOx-DLC) films get help from the environment during sliding?

248th National Meeting (2014)

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