Susceptibility to scratch damage of high density polyethylene coating

The scratch behaviour of a polymeric coating, based on high density polyethylene (HDPE), used for pipeline application was investigated in this work. Instrumented scratch testing was used for the characterization of the friction and wear behaviour of such materials. Static contact of a diamond conical indenter against the polyethylene (PE) coating was experimentally studied. Normal and tangential forces are measured during the scratch experiments using various scratch parameters (such as sliding velocity, attack angle, applied normal load). All the experiments were performed under unlubricated conditions and at room temperature. Moreover, some hygrothermally aged coating samples were considered in order to analyze the effect of immersion aging on their scratch behaviour. Before being subjected to scratch experiments, these samples were immersed in synthetic sea water at a set temperature of 70 °C and for 6 months. The scratch behaviour of the polymeric coating was discussed in terms of friction coefficient, wear resistance and wear mechanisms. Thus, scratch tracks were analyzed qualitatively and quantitatively. To characterize the scratch process, three-dimensional topography of the scratched surfaces was measured. In fact, wear morphologies of the PE coating were observed after scratching by tactile profilometer and laser interferometer. Friction response was correlated to wear mechanisms. Wear volume can be considered relevant responses to describe the materialʹs scratch resistance. It was found that friction and wear behaviours are significantly affected by scratch parameters. Hygrothermal aging considerably affects the wear resistance of the studied coating. In terms of wear mechanisms, the ploughing controls the wear of such PE coating whole the retained test conditions.