2 - Synergism effects during friction and fretting corrosion experiments – focusing on biomaterials used as orthopedic implants

Abstract

This chapter is focused on the specific phenomenon of wear (friction and fretting) and corrosion related to orthopedic implants. Both fields are closely linked through mechanical (wear) and chemical (corrosion) factors, and by mutual synergism. After defining differences between wear corrosion and fretting corrosion, we focus our attention on the synergism that exists between mechanical wear and corrosion. Careful characterization of synergistic effects has proved to be the key factor in determining the rates of tribological degradation of metals and alloys. Indeed, an insulating material, such as poly(methylmethacrylate) (PMMA), which is not susceptible to corrosion, is subjected to mechanical damage during wear or fretting. However, in the case of a metal fretting against a soft material like PMMA, the surface does not suffer purely mechanical degradation, as it is too hard and its mechanical properties (Young’s modulus, yield strength, etc.) are far superior to those of PMMA. Thus, metals suffer degradation under these circumstances when in contact with an aqueous solution, because of the conjoint action of corrosion and mechanics. Thus, this chapter is mainly focused on describing wear and fretting in a corrosive medium, their differences, and determining the effects of corrosion, mechanics and the synergistic interactions between them.