| Summary: | In our previous study, it was found that the wear life of the DLC/AlN hybrid film compared with a DLC film deposited directly onto Al-alloy could be improved by controlling the hardness of the AlN intermediate layer film. However, the hard coating like above films has a possibility to decline the fatigue strength of based material. In the present study, to ensure the fatigue reliability of Al alloy coated with DLC/AlN hardness gradient hybrid film, the fatigue strength and the fatigue failure mechanism were investigated. Fatigue strength of A7075 alloy coated with DLC/AlN hybrid film in lower stress side was higher than the untreated material, but that in higher stress side was almost the same as the untreated material. Compressive residual stress of A7075 alloy coated with DLC/AlN composite film was larger than the untreated material. From the observation of crack initiation part in the fracture surface of the A7075 alloy coated with DLC/AlN hybrid film by SEM, micro cracks in AlN film were found to be generate from the interface between Al base material and AlN film by the local plastic deformation in Al base material. Since the DLC film with a high fracture toughness values obstruct that micro cracks came out to the film surface, the initiation of a main crack was delay. As the result, the fatigue life of DLC/AlN hybrid coating material was improved. DLC/AlN hybrid coating is considered to represent a simple and effective means of improving the wear resistance and fatigue reliability of Al-alloy components commonly used within the aerospace and automotive industries.
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