title: Effect of carbon on the microstructure, mechanical properties and metal ion release of Ni-free Co-Cr-Mo alloys containing nitrogen.
abstract: This paper investigated the effect of carbon addition on the microstructure and tensile properties of Ni-free biomedical Co-29Cr-6Mo (mass%) alloys containing 0.2 mass% nitrogen. The release of metal ions by the alloys was preliminarily evaluated in an aqueous solution of 0.6% sodium chloride (NaCl) and 1% lactic acid, after which samples with different carbon contents were subjected to hot rolling. All specimens were found to primarily consist of a γ-phase matrix due to nitrogen doping, with only the volume fraction of M23C6 increasing with carbon concentration. Owing to the very fine size of these carbide particles (less than 1 μm), which results from fragmentation during hot rolling, the increased formation of M23C6 increased the 0.2% proof stress, but reduced the elongation-to-failure. Carbon addition also increased the amount of Co and Cr released during static immersion; Co and Cr concentrations at the surfaces, which increased with increasing the bulk carbon concentrations, possibly enhanced the metal ion release. However, only a very small change in the Mo concentration was noticed in the solution. Therefore, it is not necessarily considered a suitable means of improving the strength of biomedical Co-Cr-Mo alloys, even though it has only to date been used in this alloy system. The results of this study revealed the limitations of the carbon strengthening and can aid in the design of biomedical Co-Cr-Mo-based alloys that exhibit the high durability needed for their practical application.
authors.affiliation: Department of Materials and Environmental Engineering, National Institute of Technology, Sendai College, 48 Nodayama, Medeshima-Shiote, Natori 981-1239, Japan; Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Manami
authors.initials: M
authors.lastname: Mori
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan. Electronic address: k_yamanaka@imr.tohoku.ac.jp.
authors.forename: Kenta
authors.initials: K
authors.lastname: Yamanaka
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan; Eiwa Co., Ltd., 405-45 Kasshi-cho, Kamaishi 026-0001, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Kuramoto
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Kazuyo
authors.initials: K
authors.lastname: Ohmura
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Ashino
authors.affiliation: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors.forename: Akihiko
authors.initials: A
authors.lastname: Chiba
mesh_terms: D000497:Alloys / Q000737:chemistry*; D002244:Carbon / Q000737:chemistry*; D007477:Ions / Q000737:chemistry*; D008422:Materials Testing / Q000379:methods; D008670:Metals / Q000737:chemistry*; D009584:Nitrogen / Q000737:chemistry*; D013718:Tensile Strength
chemical_list: D000497:Alloys; D007477:Ions; D008670:Metals; C491689:cobalt-nickel-chromium-molybdenum alloy; D002244:Carbon; D009584:Nitrogen
keywords: Biomedical Co–Cr–Mo–N alloys; Carbon addition; Hot-rolling; Mechanical properties; Metal ion release; Precipitation