Manufacturing of high-strength Ni-free Co–Cr–Mo alloy rods via cold swaging. (July 2016)

• Record Type: Journal Article
• Authors: Yamanaka, Kenta; Mori, Manami; Yoshida, Kazuo; Kuramoto, Koji; Chiba, Akihiko
• Is Part Of: Journal of the mechanical behavior of biomedical materials. Volume 60(2016)
• Page Start: 38
• Page End: 47
• Publication Date: 2016-07
• Subjects: Biomedical Ni-free Co–Cr–Mo alloys -- Cold swaging -- Strain-induced martensitic transformation -- Deformation microstructures -- Tensile properties; Biomedical materials -- Periodicals; Biomedical materials -- Mechanical properties -- Periodicals; Biomedical materials; Biomedical materials -- Mechanical properties; Periodicals; Electronic journals; 610.28
• DOI: 10.1016/j.jmbbm.2015.12.032
• Languages: English
• ISSNs: 1751-6161

Abstract

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 1900 MPa, 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. Graphical abstract: Highlights: High-strength Ni-free Co–Cr–Mo alloy rods are prepared via cold swaging. The evolution of the rod microstructures and mechanical properties is examined. N doping is used to improve the cold deformability. A maximum reduction in area of 42.6% is obtained for the cold-swaged rods. A high 0.2% proof stress of 1900 MPa is obtained, surpassing alternative methods.