Room-Temperature Deformation and Martensitic Transformation of Two Co-Cr-Based Alloys
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to their high strength, wear and corrosion resistances, and good biocompatibility, cobalt-chromium-based alloys have long been used in medical implants, including dental,[1] orthopedic,[2] and vascular[3–5] applications. Two alloys within this cobaltchrome family are most common. ASTM F1537 calls for a weight composition of Co-28Cr-6Mo (hereinafter referred to as F1537). The alloy L605 is governed by ASTM F90 and has a composition of Co-20Cr-15W-10Ni. These alloys share some common features: at high temperatures, both alloys are single c-phase materials with an fcc crystal structure. At low temperatures, under the equilibrium condition, c-phase transforms to e-phase with an hcp crystal structure.[6] Since the fcc fi hcp isothermal phase transformation is very slow, the material normally maintains the c-phase structure after solution annealing. Depending on the
S. CAI and J.E. SCHAFFER are with the Fort Wayne Metals Research Products Corporation, 9609 Ardmore Ave., Fort Wayne, IN 46809. Contact e-mail: [email protected] D. HUANG and J. GAO are with the Key Laboratory of Electromagnetic Processing of Materials (Ministry of Education), Northeastern University, Shengyang 110819, China. Y. REN is with the APS, Argonne National Laboratory, 9700 S. Cass Ave., Argonne, IL 60439. Manuscript submitted September 19, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
processing history, secondary phases such as the athermal martensitic e-phase, r-phase, and carbides can arise; these increase the material’s strength and hardness, but decrease the ductility and toughness.[7–10] Stress-induced martensitic e-phase has been reported in both alloys, which can cause rapid hardening and embrittlement during cold forming.[11,12] While the influences of microstructure and chemistry on stress-induced martensitic transformation (SIMT) in F1537 have been investigated,[13] similar studies on L605 are rare. Despite many years of research with these materials, current micromechanical understanding of these alloys is incomplete. In the current study, in situ synchrotron X-ray diffraction tensile testing was used to observe the micromechanical behaviors of these two alloys. The data presented herein provide insight into the roles of different phases and grain families as well as the evolution of internal strains and textures during deformation at the microscopic level. Finally, these data will be useful in future Integrated Computational Materials Engineering (ICME)-based design approaches. Two commercially available materials were investigated in this study. Their chemical compositions are listed in Table I. The Ni and Fe additions to L605 give an increased austenitic stability compared with F1537.[9] In addition, L605 has a large amount of W and an elevated C content, which results in tungsten carbide (WC) precipitates after solution annealing. Wire samples of both materials with a diameter of ~ 0.45 mm were annealed at 1079 C for 20 seconds in argon atmosphere followed by a fast quench. In situ synchrotron X-ray diffraction testing was perfor
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