Crack evolution in diamond like carbon films on steel substrates during nano indentation
Abstract Fracture behaviors of thin hard diamond like carbon (DLC) films were investigated considering the effects of plastic deformation of steel substrates. Nano indentation tests for DLC films on SUS304 and M50 steels were conducted. The nucleation and propagation of film cracks were analyzed using the extended finite element method (XFEM) The ultimate tensile strength, fracture energy release rate and toughness of the films were evaluated. Results showed that cracks in DLC films on M50 steel substrates nucleated on the top surface of the films during nano indentation; however, the first crack initiated at the bottom surface of DLC films on SUS304 steel because of its low yield strength. Large plastic deformation of the steel substrate was generated under nano indentation, leading to consequent high tensile stress that concentrated first at the bottom surface of the films due to the film bending effect.