Fracture mechanics of diamond-like carbon (DLC) films coated on flexible polymer substrates

Diamond-like carbon (DLC) films have been widely used for many industrial applications due to their outstanding physical properties such as high hardness, wear resistance and biological compatibility. The DLC films coated on polymer substrates have also been extensively used and investigated because recently, quite a few applications for the use of these polymer–DLC composites have been proposed and actively discussed. The applications range from DLC-coated Polyethylene Terephthalate film (DLC-PET), through DLC-coated Polycarbonate (DLC-PC) to other DLC-coated rubbers. In this work, thin DLC films coated on several polymer substrates possessing different chemical structures and Young's moduli were introduced. The DLC-polymer films were stretched to different strains and the extended surface was investigated by optical microscopy and scanning electron microscopy (SEM) to study the fracture mechanics of the DLC-coated polymer films. Horizontally and vertically aligned micro-cracks and micro-buckling were observed, constructing periodic lattice-like fracture patterns on the surface of the extended DLC-polymer films. It was found that the lattice patterns were significantly influenced by Young's moduli of polymer substrates and DLC films, and that the patterns were also dependent on the adhesion between the DLC films and the polymers.