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Fatigue failure of hard coatings usually occurs at much lower loads than failure under static loading. Hence one way to evaluate coating adhesion should be cyclic loading close to service conditions. In this study, a new method of adhesion measurement for hard coatings is introduced based on interfacial fatigue under repeated indentation. Mono-and multi-layered coatings with different interfacial states are evaluated by a repeated-indentation test. Detachment of the coatings occurs initially at the rim of the indenter imprint, apparently as a result of adhesive failure. In contrast to monolayer coatings, peeling of multilayer coatings depends on the lowest strength of the interfaces. This study also demonstrates that the adhesion determined by the repeatedindentation test is sensitive to the interfacial state, allowing an optimised or weakened interface to be clearly revealed.

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In this study, duplex surface treatments were used to prepare a ZrO2/Cr bilayer coating on zirconium alloy cladding for enhancing the wear and corrosion behaviors. The surface and cross-section morphology of coated Zr-4 alloy was characterized; the results show that the Cr- and ZrO2/Cr-coated samples had similar morphology, and more obvious surface undulates could be observed on the ZrO2/Cr coating than the pure Cr coating owing to the rough surface of the plasma electrolytic oxidation coating. Wear and electrochemical behavior in 1200 mg/L H3BO3 and 2.2 mg/L LiOH solutions of original and coated Zr-4 alloy were investigated. The electrochemical corrosion test indicated the coated Zr-4 alloy exhibited better corrosion resistance behavior than the original Zr-4 alloy. The potentiodynamic polarization curves and corrosion morphology suggest the pitting corrosion occurred on the surface of the original and coated Zr-4 alloy. The ZrO2/Cr-coated Zr-4 alloy had better corrosion resistance due to the dual protection of the PEO layer and Cr coating. The wear behavior of the original and coated Zr-4 alloy was also investigated under a constant load of 5 N. The results reveal that the coated Zr-4 alloy had better wear resistance, and the PEO layer was found to significantly enhance the wear resistance of the Zr-4 alloy.