TABLE OF CONTENTS The practice of using metallic materials to repair or replace bones in the human body is now well established. An important parameter in determining the suitability of a material for use in surgical implants is its corrosion resistance. In many industrial applications, metal corrosion is controlled by these means: altering the local environment, changing the pH, lowering the temperature, or adding chemical inhibitors. Unfortunately, these techniques cannot be used to reduce the corrosion rate of surgical implants since the environment within the human body is fixed. Coatings (e.g., paints) are also widely used to control corrosion. However, these coatings are of limited use to protecting implants. This is because many of these implants (especially orthopedic devices) are subjected to wearing and abrasion processes that will damage most coatings [1]. The only generally successful method of reducing corrosion within the human body is to fabricate the implants from a corrosion-resistant alloy.
This approach has been extremely successful at least with respect to extending the lifetime of biomedical devices. Up to the late 1970s, corrosion of surgical implants loomed large as a major concern. The development of a range of corrosion-resistant alloys, such as Ti-6Al-4V and high-nitrogen stainless steels, have reduced the number of failures to extremely low levels. Even most of the few failures that still occur are often traced to either poor quality control (for example a 304L screw instead of a 316L screw was used), or to an unexpected and unusually aggressive local environment around the implant (due...
