Mechanisms of blistering and chipping of a scratch-resistant coating

Using a single-asperity scratching device allowing in situ observation of the scratch, the fracturing of a thin (3.5 μm) nano-composite coating deposited on a viscoelastic-viscoplastic substrate (polycarbonate) was investigated under different conditions of temperature and scratching speed. Four types of fracture mechanisms were observed, depending on these two variables. The processes involved in deformation of the system were: (i) delamination (blister formation) and fracture (chipping) of the coating and (ii) viscoelastic-viscoplastic deformation of the substrate. Image analyses were performed on video sequences of the different processes leading to damage of the film. The quantitative results are discussed in terms of the damage mechanisms involved.