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Fe‐Cr‐Al Alloy with an Alumina Layer on the Surface

The biomaterials employed for orthopedic surgery include metals (such as SUS 316L and the Co and Ti alloys), polymeric materials (such as high density polyethylene, ultra high molecular weight polyethylene, silicones, Teflon, and methylmethacrylate), and ceramics (such as alumina, zirconia, hydroxyapatite, tricalcium phosphate, and glass ceramics). Each material has its merits and demerits as a biomaterial. Therefore, in order to utilize only the good points of each, there is an increasing tendency for some kinds of materials to be combined and used as composites. For instance, metal materials have problems such as corrosion and the deposition of metallic elements in the living body, and alumina ceramics, which are quite stable in vivo, have drawbacks such as excessive hardness and brittleness. Thus, to compensate for the respective bad points, studies have been started on the coating of alumina over metallic surfaces. It is very difficult, however, to coat alumina and to prevent exfoliation from the surface. For this reason, we have not only studied the method of coating alumina from the outside, but have, for the last several years, been developing an Fe-Cr-A1 alloy that is a biomaterial having inexfoliatable alumina (a-Al,O,) deposited on the surface layer.