Manufacturing of high-strength Ni-free Co-Cr-Mo alloy rods via cold swaging

Kenta Yamanaka, Manami Mori, Kazuo Yoshida, Koji Kuramoto, Akihiko Chiba

Research output: Contribution to journalArticlepeer-review

15 Citations (Scopus)


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.

Original languageEnglish
Pages (from-to)38-47
Number of pages10
JournalJournal of the Mechanical Behavior of Biomedical Materials
Publication statusPublished - 2016 Jul 1


  • Biomedical Ni-free Co-Cr-Mo alloys
  • Cold swaging
  • Deformation microstructures
  • Strain-induced martensitic transformation
  • Tensile properties


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