Strain rate effect on the fatigue failure of thin PVD coatings: An investigation by a novel impact tester with adjustable repetitive force

Physical vapor deposition (PVD) coated surfaces are often subjected to repetitive impact loads. In such cases, the strain rate's effect on the coating fatigue failure is pivotal. This effect was investigated via a novel impact tester which facilitates the modulation of the applied impact force versus the time through an adjustable piezoelectric actuator. Using the developed test arrangement, impact loads of various patterns, frequencies and durations were generated and the coated specimens' surface response and film fatigue fracture were captured. Based on these results, it was possible to correspond impact forces of various data to equivalent quasi static ones which induce approximately the same coating and substrate deformation. At the latter loads, the coated specimen deformation was determined by Finite Element Method (FEM) calculations taking into account elastic-plastic film and substrate properties attained by an analytical evaluation of nanoindentation results. Moreover, strain, strain rate combinations insuring film fatigue endurance after one million impacts were estimated. (C) 2012 Elsevier Ltd. All rights reserved.