STP1371: The Role of Oxidation on the Thermo-mechanical Fatigue of Timetal 21S Matrix Composites

    Jin, O
    Graduate student and Professor, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA

    Johnson, WS
    Graduate student and Professor, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA

    Pages: 17    Published: Jan 2000


    Abstract

    Isothermal fatigue tests were performed on unnotched quasi-isotropic SCS-6/Timetal 21S (Ti-15Mo-2.6Nb-3Al-0.2Si) composites at room temperature, 400°C and 500°C with various hold times (0, 1 and 10 seconds). The specimen tested at 500°C showed significant oxidation, especially along the grain boundaries. In addition, there were changes in various physical properties of the composites at elevated temperatures: oxidation, phase transformation, viscoplastic flow of matrix, and interface reaction. The measurement of oxide thickness of both with and without load indicated that the oxidation of the matrix material was more severe with applied load than without load for the same amount of exposure time. Simple spectrum loading tests were conducted to examine the effect of test temperature on the formation of oxidation and its influence on the damage accumulation in the composites. Different numbers of applied cycles per block were used: n1 and n2 = 10, 100, and 1000 cycles. The change in temperature along with stress acted as thermal cycle that further introduced damages into the composites and reduced their life. As the number of applied cycles increased, the failure life of the composites was increased. The small number of cycles per block showed a shorter life due to more frequent changes in temperature level.

    Keywords:

    titanium matrix composites, silicon carbide fibers, quasiisotropic laminate, isothermal fatigue, spectrum loading, damage mechanisms, damage accumulation, oxidation, time dependent behavior


    Paper ID: STP15262S

    Committee/Subcommittee: E08.09

    DOI: 10.1520/STP15262S


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