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    STP857

    Effect of Low Temperature on Fatigue and Fracture Properties of Ti-5Al-2.5Sn(ELI) for Use in Engine Components

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    Abstract

    The results of an experimental investigation designed to obtain the material property data necessary to establish the salient characteristics of a Ti-5Al-2.5Sn(ELI) alloy for use in a fuel pump impellor at cryogenic temperatures are described. Tension, fracture toughness, and fatigue crack propagation data were obtained from pancake forgings at room temperature in laboratory air and at 20 K (−423°F) in liquid hydrogen. Experiments were performed on coupons of three different orientations, from different forgings, and from different forging lots. The effect of frequency (0.1 and 10 Hz) and R ratio (+0.05 and +0.5) on crack propagation was evaluated.

    Tensile strength significantly increased at cryogenic temperatures compared to room temperature, percent elongation had a minor reduction, percent reduction in area significantly decreased, and modulus increased approximately 8%. Fracture toughness showed a significant reduction at cryogenic temperatures, as expected. A difference in toughness caused by orientation of as much as 25% was observed, despite the lack of any significant differences in material texture. The fatigue crack growth rate of this alloy showed a remarkable lack of sensitivity to the various experimental conditions. Crack orientation effects were minimal, although there were some small shifts in threshold. The two different forging lots resulted in a small shift in growth rate. No effect of frequency was found at any combination of R ratio and temperature. A load ratio effect was observed, but this expected result was manifested only by a small shift to higher rates at R = 0.5. No effect of temperature on fatigue crack propagation was observed from threshold (∼10−8 m/cycle [∼4 × 10−7 in./cycle]) to 44 MPa √m (40 ksi √in.) (∼1 × 10−6 m/cycle [∼4 × 10−5 in./cycle]). Above this level the observed difference in growth rate was due to the lower fracture toughness at 20 K (−423°F).

    Keywords:

    mechanical properties (tensile strength, fracture toughness, fatigue crack growth), low temperature properties (titanium)


    Author Information:

    Ryder, JT
    senior research scientistgroup engineer, Lockheed-California Co.General Dynamics Convair Division, BurbankSan Diego, CACA

    Witzell, WE
    senior research scientistgroup engineer, Lockheed-California Co.General Dynamics Convair Division, BurbankSan Diego, CACA


    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP32758S