title: Development of microstructure and mechanical properties during annealing of a cold-swaged Co-Cr-Mo alloy rod.
abstract: In this study, we investigated the evolution of the microstructure and mechanical properties during annealing of a cold-swaged Ni-free Co-Cr-Mo alloy for biomedical applications. A Co-28Cr-6Mo-0.14N-0.05C (mass%) alloy rod was processed by cold swaging, with a reduction in area of 27.7%, and then annealed at 1173-1423K for various periods up to 6h. The duplex microstructure of the cold-swaged rod consisted of a face-centered cubic γ-matrix and hexagonal closed-packed ε-martensite developed during cold swaging. This structure transformed nearly completely to the γ-phase after annealing and many annealing twin boundaries were observed as a result of the heat treatment. A small amount of the ε-phase was identified in specimens annealed at 1173K. Growth of the γ-grains occurred with increasing annealing time at temperatures ≥1273K. Interestingly, the grain sizes remained almost unchanged at 1173K and a very fine grain size of approximately 8μm was obtained. The precipitation that occurred during annealing was attributed to the limited grain coarsening during heat treatment. Consequently, the specimens treated at this temperature showed the highest tensile strength and lowest ductility among the specimens prepared. An elongation-to-failure value larger than 30% is sufficient for the proposed applications. The other specimens treated at higher temperatures possessed similar tensile properties and did not show any significant variations with different annealing times. Optimization of the present rod manufacturing process, including cold swaging and interval annealing heat treatment, is discussed.
authors: Department of Materials and Environmental Engineering, National Institute of Technology, Sendai College, 48 Nodayama, Medeshima-Shiote, Natori 981-1239, Japan.
authors: Manami
authors: M
authors: Mori
authors: Department of Materials and Environmental Engineering, National Institute of Technology, Sendai College, 48 Nodayama, Medeshima-Shiote, Natori 981-1239, Japan.
authors: Nanae
authors: N
authors: Sato
authors: 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: Kenta
authors: K
authors: Yamanaka
authors: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors: Kazuo
authors: K
authors: Yoshida
authors: 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: Koji
authors: K
authors: Kuramoto
authors: Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan.
authors: Akihiko
authors: A
authors: Chiba
mesh_terms: D000497:Alloys / Q000032:analysis*; D002857:Chromium; D003035:Cobalt; D003080:Cold Temperature; D008422:Materials Testing; D008982:Molybdenum; D013718:Tensile Strength
chemical_list: D000497:Alloys; D002857:Chromium; D003035:Cobalt; D008982:Molybdenum
keywords: Cold swaging; Heat treatment; Microstructures; Ni-free Co–Cr–Mo alloys; Tensile properties