title: Manufacturing of high-strength Ni-free Co-Cr-Mo alloy rods via cold swaging.
abstract: The strengthening of biomedical metallic materials is crucial to increasing component durability in biomedical applications. In this study, we employ cold swaging as a strengthening method for Ni-free Co-Cr-Mo alloy rods and examine its effect on the resultant microstructures and mechanical properties. N is added to the alloy to improve the cold deformability, and a maximum reduction in area (r) of 42.6% is successfully obtained via cold swaging. The rod strength and ductility increase and decrease, respectively, with increasing cold-swaging reduction r. Further, the 0.2% proof stress at r=42.6% eventually reaches 1900MPa, which is superior to that obtained for the other strengthening methods proposed to date. Such significant strengthening resulting from the cold-swaging process may be derived from extremely large work hardening due to a strain-induced γ (fcc)→ε (hcp) martensitic transformation, with the resultant intersecting ε-martensite plates causing local strain accumulation at the interfaces. The lattice defects (dislocations/stacking faults) inside the ε phase also likely contribute to the overall strength. However, excessive application of strain during the cold-swaging process results in a severe loss in ductility. The feasibility of cold swaging for the manufacture of high-strength Co-Cr-Mo alloy rods is discussed.
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: Department of Materials and Environmental Engineering, National Institute of Technology, Sendai College, 48 Nodayama, Medeshima-Shiote, Natori 981-1239, 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.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Yoshida
authors.affiliation: 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: Akihiko
authors.initials: A
authors.lastname: Chiba
mesh_terms: D000497:Alloys / Q000138:chemical synthesis*; D001672:Biocompatible Materials / Q000138:chemical synthesis*; D002857:Chromium; D003035:Cobalt; D008422:Materials Testing; D008982:Molybdenum; D013718:Tensile Strength
chemical_list: D000497:Alloys; D001672:Biocompatible Materials; D002857:Chromium; D003035:Cobalt; D008982:Molybdenum
keywords: Biomedical Ni-free Co–Cr–Mo alloys; Cold swaging; Deformation microstructures; Strain-induced martensitic transformation; Tensile properties