Development of microstructure and mechanical properties during annealing of a cold-swaged Co–Cr–Mo alloy rod

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

Research output: Contribution to journalArticlepeer-review

8 Citations (Scopus)


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 1173–1423 K for various periods up to 6 h. 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 1173 K. Growth of the γ-grains occurred with increasing annealing time at temperatures ≥1273 K. Interestingly, the grain sizes remained almost unchanged at 1173 K and a very fine grain size of approximately 8 μm 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.

Original languageEnglish
Pages (from-to)187-198
Number of pages12
JournalJournal of the Mechanical Behavior of Biomedical Materials
Publication statusPublished - 2016 Dec 1


  • Cold swaging
  • Heat treatment
  • Microstructures
  • Ni-free Co–Cr–Mo alloys
  • Tensile properties

ASJC Scopus subject areas

  • Biomaterials
  • Biomedical Engineering
  • Mechanics of Materials


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