Transformation of Electron-Beam Physical Vapor-Deposited 8 wt% Yttria-Stabilized Zirconia Thermal Barrier Coatings

Authors

  • Vanni Lughi,

    Corresponding author
    1. Materials Department, College of Engineering, University of California, Santa Barbara, California 93106-5050
      †Author to whom correspondence should be addressed: e-mail: vanni@engr.ucsb.edu
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  • David R. Clarke

    1. Materials Department, College of Engineering, University of California, Santa Barbara, California 93106-5050
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  • K. T. Faber—contributing editor

  • Supported by ONR MURI.

†Author to whom correspondence should be addressed: e-mail: vanni@engr.ucsb.edu

Abstract

Yttria-stabilized (8.6 mol% YO1.5) zirconia thermal barrier coatings evolve at high temperatures from the “non-transformable,” metastable tetragonal-prime phase in their as-deposited condition to a mixture of the tetragonal and cubic phases. The kinetics of the transformation at 1200° and 1425°C are reported based on X-ray diffraction measurements. Complementary Raman spectroscopy measurements indicate a sharpening of the tetragonal bands at 263 and 465 cm−1 that is attributed to a systematic decrease in disorder of the Y3+ and oxygen vacancies with annealing. No transformation to the monoclinic form of zirconia is observed immediately after high-temperature treatment. However, partial transformation to monoclinic occurs after a prolonged time (months) at room temperature in those samples treated at 1425°C, indicating the development of isothermal martensite.

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