Toughness Properties of a Silicon Carbide with an in Situ Induced Heterogeneous Grain Structure

Authors

  • Nitin P. Padture,

    1. Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
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      Member, American Ceramic Society.

    • Guest Scientist, on leave from Department of Materials Science and Engineering. Lehigh University. Bethlehem, PA 18015.

  • Brian R. Lawn

    1. Materials Science and Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899
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      Member, American Ceramic Society.


  • G. Grathwohl—contributing editor

  • Supported by the U.S. Air Force Office of Scientific Research.

Abstract

Toughness characteristics of a heterogeneous silicon carbide with a coarsened and elongated grain structure and an intergranular second phase are evaluated relative to a homogeneous, fine-grain control using indentation–strength data. The heterogeneous material exhibits a distinctive flaw tolerance, indicative of a pronounced toughness curve. Quantitative evaluation of the data reveals an enhanced toughness in the long-crack region, with the implication of degraded toughness in the short-crack region. The enhanced long-crack toughness is identified with crack-interface bridging. The degraded short-crack toughness is attributed to weakened grain or interface boundaries and to internal residual stresses from thermal expansion mismatch. A profound manifestation of the toughness-curve behavior is a transition in the nature of mechanical damage in Hertzian contacts, from classical single-crack cone fracture in the homogeneous control to distributed subsurface damage in the heterogeneous material.

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