The environment in a living body is severely corrosive to
metallic materials. On top of that, many of the components are
used under mechanical load. In particular, artificial hip joints,
etc are loaded repeatedly during walking. Thus, metallic
biomaterials are required to have not only excellent corrosion
resistance but also excellent corrosion fatigue properties.
Furthermore, fretting damage occurs when two components
in contact with each other are loaded repeatedly, for instance,
in the case of a bone plate and a screw used for fracture
treatment. Fretting causes continuous removal of surface
oxide films, so that the fretting in a corrosive environment
enhances corrosion damage and corrosion enhances fretting
wear. The synergistic phenomenon is called tribocorrosion.
The tribocorrosion generally promotes the fatigue damage
of the materials. As well as the friction stress added to the
cyclic axial stress, surface tribocorrosion damage is one of
the reasons why corrosion fatigue strength accompanied by
fretting (fretting corrosion fatigue strength) is generally lower
than conventional corrosion fatigue strength [12].