Hydrogen Embrittlement of Zimaloy: A Cobalt-Chromium-Molybdenum Orthopedic Implant Alloy

    Published: Jan 1985

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    Controlled potential, slow strain rate tests of Zimaloy (a cobalt-based orthopedic implant alloy) in Ringer's solution (a physiological saline solution) at 37°C show that hydrogen absorption may degrade the mechanical properties of that alloy. Potentials were controlled so that the tensile sample was either cathodic or anodic with respect to the metal's free corrosion potential. Hydrogen was generated on the sample surface when the specimen was cathodic, and dissolution of the sample was encouraged when the sample was anodic. The results of these controlled potential tests showed no susceptibility of this alloy to stress corrosion cracking at anodic potentials.

    However, when samples were tested at a potential of 150 mV cathodic to the free corrosion potential, the difficulty was decreased by 37%. The 150-mV shift in potential was selected because that was the potential observed when this alloy, in a creviced condition, was placed in Ringer's solution for two months. Support for this reduction in ductility during the cathodic exposures was obtained by testing the hydrogen compatibility of the alloy. Samples charged in gaseous hydrogen showed significant losses in ductility. The most severe hydrogen charging (207 MPa at 300°C for ten days) reduced the tensile ductility to 0% reduction in the area at fracture while less severe charging (6.9 MPa at 200°C for seven days) caused a 50% decrease in ductility. Results of these tests indicate that this cobalt-based alloy suffers a significant loss in ductility under conditions that may arise if a creviced sample is exposed to saline solutions.


    hydrogen embrittlement, polarization, tension tests, crevice potential, Zimaloy, cobalt-chromium-molybdenum alloy, implant materials, fatigue (materials), degradation

    Author Information:

    Edwards, BJ
    Graduate student and professor, Virginia Polytechnic Institute and State University, Blacksburg, VA

    Louthan, MR
    Graduate student and professor, Virginia Polytechnic Institute and State University, Blacksburg, VA

    Sisson, RD
    Professor, Worcester Polytechnic Institute, Worcester, MA

    Committee/Subcommittee: F04.19

    DOI: 10.1520/STP33239S

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