STP684: Corrosion Fatigue of 316L Stainless Steel, Co-Cr-Mo Alloy, and ELI Ti-6Al-4V

    Imam, MA
    Research scientist and associate professor, School of Engineering and Applied Science, The George Washington University, Washington, D.C.

    Fraker, AC
    Metallurgist, National Bureau of Standards, Washington, D.C.,

    Gilmore, CM
    Research scientist and associate professor, School of Engineering and Applied Science, The George Washington University, Washington, D.C.

    Pages: 16    Published: Oct 1979


    Abstract

    The purpose of this paper is to compare corrosion-fatigue properties of selected implant alloys and to discuss the corrosion fatigue-life in terms of the corrosion behavior and the metal microstructure. The tests were conducted in fully reversed torsion in flowing Hank's solution at a temperature of 37°C and a pH of 7.4. Specimens were subjected to fatigue at shear strains ranging from 0.006 to 0.018 and at a frequency of 1 Hz. Surfaces of the 0.5-cm-diameter specimens were prepared by mechanically polishing through a 0.05 alumina powder and following this with steam sterilization.

    During the tests, the specimen electrode potentials versus time were monitored on a strip chart recorder. The potential-time curves for the metals studied show the establishment of a steady rest potential which does not change until the fatigue motion has been applied. The potential then goes in the negative direction. The rate of this decline in potential appears to-be related to the metal microstructure as well as to the alloy composition. This electronegativity of the potential-time curves indicated the formation of cracks in the oxide film. These curves were more electronegative with increased shear strain, and the curves were different for the different metals tested.

    Fatigue results of these tests show that the ELI Ti-6Al-4V has the longest fatigue life under these conditions. The fatigue strength of the Ti-6Al-4V can be increased many times by changing the microstructure through heat treating and quenching. The Type 316L stainless steel had the next longest fatigue life. The cast Co-Cr-Mo alloy had the shortest fatigue life and also showed more scatter in the results. Other workers have shown that further heat treating and processing improves the fatigue resistance of this material too.

    Keywords:

    implant materials, corrosion, fatigue (materials), metal implants, 316 stainless steel, titanium-6 aluminum-4 vanadium alloy, cobalt-chromium-molybdenum alloy


    Paper ID: STP35941S

    Committee/Subcommittee: F04.19

    DOI: 10.1520/STP35941S


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