Thermal expansion of EB-PVD yttria stabilized zirconia

摘要

Yttria stabilized zirconia (YSZ) layers, suited for thermal barrier coatings (TBCs) in turbine engines, were produced by electron-beam physical vapour deposition (EB-PVD) on metallic (Ni-based alloys) ceramic (Al_2O_3 ) substrates (typically at 1000℃) using ingot compositions of about 4 mol% Y_2O_3-ZrO_2 . Employing powdered samples, removed from the surface of the as-deposited YSZ layers, precision X-ray diffraction data sets were recorded between 60 and 900 ℃ and the lattice parameters of the metastable, tetragonal (t') and the cubic (c) phases were refined using Rietveld's method. It was unambiguously verified that phase (c) was present in all investigated samples as a minority phase already in the as-deposited state. The thermal expansion coefficients of the tetragonal phase (t') (α_(11) = 9.3(2) × 10~(-6) K~(-1) , α_(33) =10.8(1) × 10~(-6) K~(-1)) and the cubic phase (c) (α_(11) = 8.5(2) × 10~(-6) K~(-1) ) were evaluated from the refined temperature dependent lattice parameter values of this study, and turned out to be close to each other, but significantly different from the coefficient of the monoclinic phase (m) (α_(11) = 9.0 × 10~(-6) K~(-1) , α_(22) = 1.2 × 10~(-6) K~(-1), α_(33) =11.9 × 10~(-6) K~(-1), α_(13) =0.0 × 10~(-6) K~(-1) ), which was derived from temperature dependent lattice parameter measurements published by Touloukian et al.~5 The expansion coefficient of the monoclinic phase (m) exhibited a very pronounced anisotropy in contrast to the tetragonal phases (t') and (t). Our values for (t') and (c) were in excellent agreement with that of other tetragonal and cubic phases from the literature with quite different Y_2O_3 contents.