Microstructure and Cyclic Oxidation of Yttria-Stabilized Zirconia/Nanostructured ZrO 2 9.5Y 2 O 3 5.6Yb 2 O 3 5.2Gd 2 O
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JMEPEG https://doi.org/10.1007/s11665-020-05174-1
Microstructure and Cyclic Oxidation of Yttria-Stabilized Zirconia/Nanostructured ZrO2 9.5Y2O3 5.6Yb2O3 5.2Gd2O3 Thermal Barrier Coating at 1373 K M. Bahamirian, S.M.M. Hadavi, M. Farvizi, A. Keyvani, and M.R. Rahimipour (Submitted February 21, 2020; in revised form July 24, 2020; Accepted: 8 September 2020) 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 (apc ffiffi2 < 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. Keywords
high-temperature oxidation, mechanical and thermomechanical properties, nanostructured ZrO2 9.5Y2O3 5.6Yb2O3 5.2Gd2O3, TBCs, YSZ
1. Introduction Thermal barrier coatings (TBCs) have been developed for the protection of superalloys, especially in gas turbine and aviation engine parts from higher operating temperatures (Ref 1-4). Most of the common TBCs usually include an oxidation resistant bond coat with MCrAlY composition (M could be Co, Ni or a combination of both of them) and a high-temperature resistant ceramic top coat which is generally made of yttriastabilized zirconia (YSZ) which are deposited by thermal spray processes on the surface of superalloys (Ref 2, 5-7). However, the application of YSZ at higher temperatures ( 1473 K) has been limited due to low sintering resistance of this compound (Ref 8-11) and its susceptibility to oxygen diffusion and also, attack of certain corrosive species (Ref 7, 12, 13). Also, in YSZ TBCs, with the increment of temperature to higher than 1473 K, the tetragonal phase will transform to the cubic ZrO2 phase and upon cooling to room temperature, M. Bahamirian, Department of Mining and Metallurgical Engineering, Yazd University, Yazd, Iran; S.M.M. Hadavi, Department of Materials Engineering, University of Tarbiat Modares, Tehran, Iran; M. Farvizi, and M.R. Rahimipour, Department of Ceramics, Materials and Energy Research Center, Karaj, Iran; and A. Keyvani, Department of Metall
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