Fracture Mechanism of Diamond Like Carbon (DLC) Film Subjected to Contact Loading
Akio YONEZU, Tomoyuki NAKAYAMA and Takeshi OGAWA
Abstract:This paper discussed the fracture mechanism of diamond like carbon (DLC) film subjected to contact loading. The DLC films with over 10μm thick were deposited onto stainless steel (SUS304) by Radio Frequency (RF) plasma-based ion implantation method with different applied voltage of -20, -15 and -10 kV. Rockwell indentation tests with simultaneous monitoring of acoustic emission (AE) and corrosion potential fluctuation (CPF) techniques were applied to the DLC films to clarify the mechanism of contact fracture. The DLC films were found to produce two types of crack morphology. One is general ring crack produced by tensile stress developed around contact area of indenter under loading process. The other indicated spiral crack morphology. This crack was found to be produced under unloading process detected by AE and CPF analyses, which could determine the indentation force, Fu, at the onset of spiral crack. The values of Fu are strongly dependent on the maximum indentation force and coating process. Finite element analysis suggested that the DLC deformed plasticaly prior to the tensile fracture under loading process. Due to this plastic strain, the film buckling occurred under unloading process and resulted in the delamination and the spiral crack. Rockwell indentation method with AE and CPF monitoring system could determine the onset of film fracture, which enabled us to discuss the detailed fracture mechanism. Key Words:Diamond like carbon film, Contact fracture, Indentation, Delamination, Buckling, Acoustic emission, Corrosion potential fluctuation