7. Co-Cr Alloys as Effective Metallic Biomaterials

Because of their excellent mechanical properties, high corrosion resistance, and high wear resistance, Co-Cr alloys have been recognized as effective metallic biomaterials and have been used as materials for dental and medical devices since a cast Co-Cr-Mo alloy, Vitallium, was developed in the 1930s. Further increases in the usage of Co-Cr alloys are still expected as well. In this chapter, first, the history and current status of biomedical Co-Cr alloys such as Co-28Cr-6Mo and Co-20Cr-15W-10Ni alloys are reviewed. Their microstructure, processing, and properties are then discussed. Control of the microstructure by optimization of chemical composition of the alloys and thermomechanical treatments is described, and newly developed processing techniques for grain refinement and newly found precipitates such as the π-phase and χ-phase are discussed. As a novel process for implant fabrication, an additive manufacturing technique using an electron beam and a laser beam is mentioned. Finally, the mechanical properties and corrosion and wear resistances of the alloys are presented, and the relationships between the microstructure and properties of the Co-Cr alloys are discussed.