Tensile Stress Evolution During the Early-Stage Constrained Sintering of Gadolinium-Doped Ceria Films

Authors

  • Brian W. Sheldon,

    Corresponding author
    1. School of Engineering, Brown University, Providence, Rhode Island 02912
      †Author to whom correspondence should be addressed. e-mail: Brian_Sheldon@brown.edu
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    • *Member, American Ceramic Society.

  • Jason D. Nicholas,

    1. Lawrence Berkeley National Laboratory, Materials Sciences Division, University of California, Berkeley, California 94720
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    • *Member, American Ceramic Society.

    • Present address: Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, MI 48824.

  • Sunil Mandowara

    1. School of Engineering, Brown University, Providence, Rhode Island 02912
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  • R. Bordia—contributing editor

  • This work was supported by NSF, under awards DMR-0805172 and DMR-0520651 (MRSEC). Microscopy work was performed in the EPIC facility of Northwestern University's NUANCE Center (supported by NSF-NSEC, NSF-MRSEC, the Keck Foundation, the State of Illinois, and Northwestern University).

†Author to whom correspondence should be addressed. e-mail: Brian_Sheldon@brown.edu

Abstract

In situ measurements during the constrained sintering of Gd-doped ceria reveal tensile stresses up to ∼250 MPa. These large tensile stresses are likely to contribute to the reduced densification (compared with freely sintered material) typically observed during constrained sintering. While existing models postulate that the tensile stress in a densifying constrained film cannot exceed the “sintering stress,”σS, the observed tensile stresses are significantly larger than the estimated σS for these materials. To explain this observation, we propose that the formation and extension of interparticle grain boundaries induce substantial tensile stresses in constrained films. A model of this phenomenon shows that converting excess surface energy to elastic strain energy can produce stresses that are comparable to the measured values. Further, if these “cohesive” stresses exceed σS, grain-boundary diffusion should initially move material from the neck regions into the grain boundaries, not out of the grain boundaries as described by traditional sintering models.

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