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Microstructure and Cyclic Oxidation of Yttria-Stabilized Zirconia/Nanostructured ZrO2 9.5Y2O3 5.6Yb2O3 5.2Gd2O3 Thermal Barrier Coating at 1373 K

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Abstract

This study is intended to improve the high-temperature oxidation of nano-ZGYbY: ZrO2 9.5Y2O3 5.6Yb2O3 5.2Gd2O3 in order to apply it in the new generation of defect cluster thermal barrier coatings (TBCs) through the employment of an intermediate conventional yttria-stabilized zirconia (micro-YSZ) layer between the bond coat (CoNiCrAlY) and top coat. The specimens were deposited with an atmospheric plasma spray (APS) process on IN738LC superalloy. The cyclic oxidation test was performed in air at 1373 K with 4 h in each cycle. The microstructure of the nano-ZGYbY was studied by field emission scanning electron microscopy, revealing the formation of a bimodal microstructure consisted of nanosized particles retained from the initial APS-processed nanopowder and columnar grains, whereas the microstructure of intermediate micro-YSZ layer consisted of columnar grain splats only. X-ray diffraction of TBCs confirmed the formation of non-transformable (t′) ZrO2 phase (\( \frac{c}{a\sqrt 2 } \) < 1.01) as well as the stability of this phase after oxidation. Also, applying an intermediate conventional YSZ layer with a higher CTE and KIC than that of nano-ZGYbY between the bond and top coats improved mechanical properties in new TBCs and it increased the oxidation life.

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Authors and Affiliations

  1. Department of Mining and Metallurgical Engineering, Yazd University, Yazd, Iran

    M. Bahamirian

  2. Department of Materials Engineering, University of Tarbiat Modares, Tehran, Iran

    S. M. M. Hadavi

  3. Department of Ceramics, Materials and Energy Research Center, Karaj, Iran

    M. Farvizi & M. R. Rahimipour

  4. Department of Metallurgy and Materials Engineering, Faculty of Technology and Engineering, Shahrekord University, Shahrekord, Iran

    A. Keyvani

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Appendix

Appendix

According to Ref. 78, to measure the hardness of the coatings, micro Vickers method was employed. 300 gf load and loading time of 10 s were used for this purpose. Eq 4 was used for hardness calculation.

$$ H_{\text{V}} = 0.0018544\frac{P}{{d^{2} }} $$
(4)

In this equation, “HV” represents Vickers hardness, “P” denotes the load in “gf,” and “d” stands for the mean diameter effect of indentation in “mm”.

Elastic modulus was measured using Knoop indentation test. For which, Eq 5 was used.

$$ \frac{{b^{{\prime }} }}{{a^{{\prime }} }} = \frac{b}{a} - \alpha \frac{H}{E} $$
(5)

In this equation, \( \frac{b}{a} \) = 0.141 which is related to the geometry of indenter and also, “a′” and “b′” are the effect of indentation diameters. In this equation, “H” was obtained according to Vickers indenter to calculate elastic modulus (E). “α” was considered constant 0.45.

Crack length measurement can be used in Vickers hardness test to determine fracture toughness of ceramics. Fracture toughness of the specimens can be measured by Eq 6.

$$ K_{\text{IC}} = 0.0154\frac{P}{{C^{1.5} }}\left( {\frac{E}{H}} \right)^{0.5} $$
(6)

where “KIC” denotes fracture toughness; “P” and “C” are indenting load and mean length of crack, respectively. “H” and “E” also show Vickers hardness and Young’s modulus, respectively.

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Bahamirian, M., Hadavi, S.M.M., Farvizi, M. et al. Microstructure and Cyclic Oxidation of Yttria-Stabilized Zirconia/Nanostructured ZrO2 9.5Y2O3 5.6Yb2O3 5.2Gd2O3 Thermal Barrier Coating at 1373 K. J. of Materi Eng and Perform 29, 7080–7093 (2020). https://doi.org/10.1007/s11665-020-05174-1

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