Effects of PVD DLC coating on 7075-T6 fatigue strength at high and low number of cycles

Despite its high tensile strength and its brilliant fatigue behaviour, 7075-T6 aluminium alloy usage is dramatically reduced, due to its sensitivity to corrosion and its poor surface characteristics. In order to be adopted for advanced applications in the aeronautic, automotive and maritime fields, as well as in further innovative applications, 7075-T6 resistance must be improved. Controversial results are found in literature on coated 7075-T6 fatigue strength, due to the complex mechanical interaction between the substrate and the coating, and the high temperatures involved in the coating process. In the present work, testing on rotating bending fatigue (R = -1) 7075-T6 uncoated and PVD DLC coated specimens has been conducted. Different stress levels were considered, to assess the impact of the applied stress on the fatigue life of the substrate-coating system. SEM characterization of the fracture surfaces has been performed, to investigate the influence of the coating on the fracture mechanism.