Alloy design and microstructure of a biomedical Co-Cr alloy

Abstract

Two wrought Co-Cr alloys for dental and surgical implant and equipment applications were designed and their microstructures and hot workability determined and compared to a current dental alloy SC-H. The chemical composition of the alloys was selected with regard to the general requirements for biomedical alloys and the general principles of alloying theory. A phase-control law originally developed for nickel-base superalloys, PHACOMP, was utilized in order to avoid the formation of topologically close-packed (tcp) phases and to ensure the ductility and workability of the alloy. The alloys were cast using a vacuum induction melting technique which was found to allow a fairly good chemical composition control of the alloys. Hot forging of the as-cast alloys confirmed their good workability. Optical metailography showed the as-cast alloys to have a dendritic structure with some spherical carbide particles in the interdendrite regions. In contrast, the dental alloy SC-H in the as-cast condition had continuous carbide along the grain boundaries which impaired the ductility and prevented hot forging of this alloy die to cracking of the specimens. X-ray diffraction analysis showed that both alloys I and II have the fcc-Co matrix and Cr23C6 type carbide particles. No tcp phases were observed.