Cavitation resistance of epoxy-based multilayer coatings: Surface damage and crack growth kinetics during the incubation stage

• A linear model for crack growth as a function of cavitation time was proposed.
• Crack growth depends mainly on H/E ratio and thickness.
• The initial cracks nucleate at pre-existent stress concentrators.
• Main damage mechanisms are branching of main cracks, plastic deformation and crazing.

Four epoxy-based multilayer coating systems, with thicknesses of 380±20 μm, 650±10 μm, 720±30 μm and 920±20 μm, were applied manually onto stainless steel samples and subjected to vibratory cavitation tests according to ASTM G32-09 standard. In order to correlate the cavitation resistance of the coating systems with some of their mechanical properties, instrumented micro indentation tests were performed to determine hardness, resilience, total plastic work, among others, as a function of the thickness of the coatings. Examination of the surfaces by Scanning Electron Microscopy (SEM) revealed that the surface damage in all the coatings was caused by incubation and growth of cracks. Statistical analysis of crack growth data allowed determining a behavior law characteristic for each coating system, which was adjusted with proper parameters related to the mechanical properties measured by micro indentation. In particular, a good correlation was obtained among cavitation resistance, coating thickness and hardness-to-Young modulus ratio H/E.