A DLC (Diamond Like Carbon) film is one of the carbon-based hard films having low friction coefficient and high wear resistance. For applying to machine elements under high contact pressure, however, DLC films are required to have better mechanical properties. In the present paper, six kinds of DLC films including Cr/C gradient interlayer were deposited by UBM sputtering method in which substrate bias voltage was changing. And rolling contact tests were performed under contact pressure 2.84GPa, and tribological properties of these films were examined. It was found that friction coefficients of films were unstable when sliding contact occurred together, and fractures in their Cr/C gradient interlayers were observed. Estimating of mechanical properties of the interlayer using nanoindentation test, hardness and Young's modulus of the interlayer increased. However, they decreased less than 0.09μm depth. There change was thought to cause the fracture in the interlayer by rolling contact.
