Crystallite and Grain-Size-Dependent Phase Transformations in Yttria-Doped Zirconia

Authors

  • Arun Suresh,

    1. Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802
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    • Now at Analog Devices, Inc., Wilmington, MA 01887.

  • Merrilea J. Mayo,

    1. Department of Materials Science and Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802
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    • *

      Member, American Ceramic Society.

    • Currently adjunct to the University of Maryland, Dept. of Materials and Nuclear Engineering, College Park, MD 20742-2115.

  • Wallace D. Porter,

    1. High Temperature Materials Laboratory, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
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  • Claudia J. Rawn

    1. High Temperature Materials Laboratory, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831
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  • M. Frey—contributing editor

  • Supported by the U. S. Dept. of Energy, under Contract No. DE-FG02-98ER45700 and the High Temperature Materials Laboratory User Program, Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U.S. Dept. of Energy, under Contract No. DE-AC05-00OR22725.

Abstract

In pure zirconia, ultrafine powders are often observed to take on the high-temperature tetragonal phase instead of the “equilibrium” monoclinic phase. The present experiments and analysis show that this observation is one manifestation of a much more general phenomenon in which phase transformation temperatures shift with crystallite/grain size. In the present study, the effect of crystallite (for powders) and grain (for solids) size on the tetragonal → monoclinic phase transformation is examined more broadly across the yttria–zirconia system. Using dilatometry and high-temperature differential scanning calorimetry on zirconia samples with varying crystallite/grain sizes and yttria content, we are able to show that the tetragonal → monoclinic phase transformation temperature varies linearly with inverse crystallite/grain size. This experimental behavior is consistent with thermodynamic predictions that incorporate a surface energy difference term in the calculation of free-energy equilibrium between two phases.

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