A Study on the improvement of the tribological properties of aluminum alloy by micro-arc oxide method

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Aluminum alloys have an inherently poor wear resistance. In order to improve the wear resistance of aluminum alloy, we selected hard thin film (TiN) coating method. As the results, it was clarified that the wear resistance increased due to coating the TiN thin film onto aluminum alloy, but the TiN film fractured in short sliding distance. This is a problem to apply the aluminum alloy. In order to suppress the fracture of film, we selected the CrN film, which is high toughness ceramics, and the tribological properties were examined.A series of surface polished JIS A2024 aluminum alloy were Arc Ion Plating (AIP) coated with TiN and CrN thin films. A ball on disk tests were used CSME tribometer to evaluate tribological properties between coated aluminum disks and bearing steel (JIS SUJ2) balls. The tribological tests showed that the wear volume of CrN coated aluminum disk was smaller than that of TiN coated one. In addition, the wear volume of bearing steel ball against the CrN thin film was also decreased in comparison with TiN thin film. And the TiN coated disks were fractured by IN normal load, but the CrN coated disks were endured until 3N. The results of scratch tests also showed mat the CrN thin film was high delamination resistance. Hence, the endurance of CrN thin film was produced by the high delaminating resistance.Successive observations of wear tracks of disks and balls were carried out. The wear tracks of ball against the TiN thin film coated disk showed the typical feature of abrasive wear, and that against the CrN thin film coated one showed smooth surface caused by adhesion wear. These facts shows that the direct contact occurred between film and ball in the case of TiN thin film, and in the case of CrN thin film, the contact occurred between ball and adhesion layer. This is a cause of difference of wear properties between CrN and TiN thin film.