STP1297

    Oxidation and Mechanical Damage in a Unidirectional SiC/Si3N4 Composite at Elevated Temperature

    Published: Jan 1997


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    Abstract

    The results of a study on the high-temperature damage mechanisms in a unidirectional Nicalon fiber-reinforced reaction-bonded silicon nitride (RBSN) composite are presented in this paper. The microstructure of the as-manufactured and tested specimens were characterized using a variety of techniques including: X-ray diffraction; optical, scanning, and transmission microscopy; and dilatometry. Single-edge notch specimens under three-point bend loading were tested under a constant displacement-rate condition as well as under a sustained loading condition at 1000°C in air. The load-line displacement was used as the in situ indicator of damage accumulation. The fracture surface and the damage zone around the main crack were characterized in the fractured specimens to investigate the high-temperature fracture mechanisms. Under constant displacement rate, the composite showed extensive nonlinear load versus displacement behavior, indicating that the presence of the fiber has indeed toughened the composite. Cracks propagated nominally along the notch plane, though some delaminations were also observed. The substantial bulk oxidation occurred even at test temperatures as low as 800°C and resulted in significant changes in the dimension of the composite specimens. The fiber pullout, fracture surface morphology, and delamination were all strongly influenced by the high temperature oxidation.

    Keywords:

    ceramic matrix composite, reaction-bonded silicon nitride, Nicalon fiber, oxidation, damage, creep, cracks


    Author Information:

    Yang, F
    Ph.D. candidate, professor and chairman, and principal research scientist, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA

    Saxena, A
    Ph.D. candidate, professor and chairman, and principal research scientist, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA

    Starr, TL
    Ph.D. candidate, professor and chairman, and principal research scientist, School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA


    Paper ID: STP16325S

    Committee/Subcommittee: E08.09

    DOI: 10.1520/STP16325S


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