STP1263

    Coating Effects on Crack Growth in a Single Crystal Nickel Based Alloy During Thermo-Hechanical Fatigue

    Published: Jan 1996


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    Abstract

    Single crystal specimens of the nickel based alloy SRR99 with [001] orientation are subjected to TMF cycling between 300‡C and 1050‡C, using a −135‡lag between temperature and mechanical strain, and various R ratios. The in-situ observation of the test specimen by means of a computer vision system during TMF testing enables the initiation of microcracks to be detected when cracks have reached lengths of approximately 30 μm at the surface. High densities of point initiated micro-cracks are generated during the early stages of the TMF life. Crack increment measurements reveal marked differences between the growth rates of individual micro-cracks. The presence of a nickel-aluminide coating consistently reduces the TMF life, due largely to higher growth rates of the main crack in the substrate. In order to estimate the influence of initial crack distribution and density on life, a two dimensional crack shielding model is incorporated in a computer programme which is used to simulate the growth of interacting, parallel surface cracks. The effect of various parameters, including the density and the initial distribution of the microcracks, on the life spent to grow a crack to a pre-defined length, are discussed and the model predictions are compared with the experimental observations.

    Keywords:

    Thermo-mechanical fatigue, aero engines, micro-cracking, superalloy, single crystal, coating, crack shielding, multiple cracking, life assessment, surface crack


    Author Information:

    Bressers, J
    Institute for Advanced Materials, Joint Research Centre, Petten,

    Martinez-Esnaola, JM
    Centro de Estudios e Investigaciones Técnicas de Guipuzcoa (CEIT), San Sebastián,

    Martin-Meizoso, A
    Centro de Estudios e Investigaciones Técnicas de Guipuzcoa (CEIT), San Sebastián,

    Timm, J
    Institute for Advanced Materials, Joint Research Centre, Petten,

    Arana-Antelo, M
    Centro de Estudios e Investigaciones Técnicas de Guipuzcoa (CEIT), San Sebastián,


    Paper ID: STP16448S

    Committee/Subcommittee: E08.06

    DOI: 10.1520/STP16448S


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