The wear and friction of diamond-like nanocomposite (DLN) film have been investigated in air with different relative humidity (RH), under deionized (DI) water and saline solution. The structure of the film has been characterized by Fourier transform infrared (FTIR), Raman spectroscopy, and scanning electron microscope (SEM). The result shows two interpenetrating network structure: a–C:H and a–Si:O, and they are interpenetrated by Si–C bonding. The tribological performance has been measured using ball-on-disc tribometer with tungsten carbide ball as counterbody at 10？N normal load. Results show that with increasing relative humidity (RH) from 35% to 80%, the coefficient of friction (COF) increases gradually from 0.005 to 0.074, whereas with increasing RH the wear factor decreases from ？mm3/Nm and attains a minimum value of ？mm3/Nm at 50%？RH. With further increase of RH the wear factor increases again. Moreover, in DI water and especially in saline solution, both the COF and wear factor have been found to be significantly low. A clue has been interpreted to understand environmental dependency, considering the effect of surface dangling bonds, charge transfer, and chemical interactions. 1. Introduction Diamond-like nanocomposite (DLN) film comprises of two amorphous interpenetrating network structures: one is “diamond-like” (a-C:H) network, and the other is “glass-like” (a-Si:O) network [1–4]. The presence of a-Si:O network as a reinforcement matrix distinguishes the DLN film from conventional diamond-like carbon (DLC) film [5, 6]. The material possesses a number of unique bulk and surface properties like hardness with flexibility [7], thermal stability [7, 8], corrosion and wear resistance [8, 9], biocompatibility [10, 11], and so forth. The low residual stress and good adherence to any type of substrates make DLN film a potent material for a variety of tribological applications. It is believed that the tribological properties of the film are not only inherent properties of the film. They also strongly depend on the surrounding environment and counterbody. Many researchers have reported the dependency of environment on tribological behavior of DLC film [12, 13], though limited reports have been published particularly for DLN film. Neerinck et al. have reported that the COF of the DLN film against steel ball at 50% RH varied from 0.04 to 0.08 and remains less than 0.1 even at 90% RH. They have also observed that film wear factor was extremely low under water [14]. Scharf et al. have also reported that COF increased from 0.02 to 0.2 when the RH changed from
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