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    Influence of Microstructure on Elevated-Temperature Fatigue Resistance of a Titanium Alloy

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    The strain-controlled, elevated-temperature, low-cycle fatigue behavior of a near α titanium alloy, Ti-6Al-2Sn-4Zr-2Mo-0.1Si (Ti-6242S), has been studied in both air and vacuum (10−5 torr) at 525°C over a range of frequency and strain. Of particular interest in this investigation were the influence of microstructure and environment on fatigue behavior. Two different microstructures were obtained by combinations of mechanical processing and heat treatment above and below the β-transus temperature. Particular attention was given to these microstructural variations and to the effect of environment on the high-temperature low-cycle fatigue behavior of this alloy. The nature of fatigue crack initiation sites was examined by a precision sectioning method. The microstructure was found to have a pronounced effect on fatigue life as well as on the fatigue crack initiation process. Tests performed in vacuum revealed no influence of frequency on fatigue life, which indicated that environmental factors were responsible for the observed frequency effect on tests performed in air. It was also observed that testing in vacuum led to the formation of a number of subsurface crack nucleation sites and to a longer fatigue life. Crack origins in specimens tested in air were located at the surface, and the initiation sites were larger than those observed in vacuum. The features of a fatigue resistant microstructure in addition to environmental effects at elevated temperature are identified and discussed.


    fatigue (materials), titanium alloys, elevated temperature, microstructure, crack initiation, subsurface cracking

    Author Information:

    Hoffmann, C
    Graduate Assistant and Professor, University of Connecticut, Storrs, Ct.

    Eylon, D
    Metcut-Materials Research Group, Wright-Patterson Air Force Base, Ohio

    McEvily, AJ
    Graduate Assistant and Professor, University of Connecticut, Storrs, Ct.

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP32420S