Blistering and spalling of thin hard coatings submitted to repeated impacts

The endurance life of thin DLC coatings, obtained by plasma assisted chemical vapour deposition (PACVD), has been evaluated under repeated impact conditions. The observations of the damaged surfaces have permitted to identify several failure mechanisms. Impact tests, interrupted after various test durations, enable us to clarify the damage origin and to follow the failure evolution up to the complete coating failure. In particular, a blistering phenomenon has clearly been revealed. Some hypotheses for this unusual behaviour are proposed in reference to the film mechanical properties and residual stresses level.