Hot corrosion behavior of ZrO 2 9.5Y 2 O 3 5.6Yb 2 O 3 5.2Gd 2 O 3 TBCs in CMAS: CaO-MgO-Al 2 O 3 -SiO 2
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RESEARCH
Hot corrosion behavior of ZrO2 9.5Y2O3 5.6Yb2O3 5.2Gd2O3 TBCs in CMAS: CaO-MgO-Al2O3-SiO2 M. Bahamirian 1
&
S. M. M. Hadavi 2 & M. Farvizi 3 & A. Keyvani 4 & M. R. Rahimipour 3
Received: 13 May 2020 / Revised: 18 September 2020 / Accepted: 7 October 2020 # Australian Ceramic Society 2020
Abstract Improvement of hot corrosion resistance in calcium-magnesium-aluminosilicate (CMAS: CaO-MgO-Al2O3-SiO2) environments is one of the main goals in the development of aero-engines especially in their thermal barrier coatings (TBCs). In this regard, this study aims to improve the quality and efficiency of the yttria-stabilized ZrO2 (8YSZ) TBCs by substitution of new coatings such as ZGYbY: ZrO2 9.5Y2O3 5.6Yb2O3 5.2Gd2O3. For this purpose, 8YSZ and ZGYbY topcoats with CoNiCrAlY bond coat were applied on IN738LC substrates using atmospheric plasma spray (APS) technique. Hot corrosion behavior of the coatings was investigated in CMAS environment by a furnace method at 1150 °C in the 4-h cycles. Phase and microstructural investigations of the coatings by XRD and FESEM/EDS methods before and after the hot corrosion test indicated the better performance of ZGYbY coating (relative to 8YSZ) in preventing from the diffusion of the CMAS particles. This could be due to the formation of the impermeable apatite compounds (i.e., Ca4Y(Yb/Gd)6O(SiO4)6). Furthermore, the destruction of the TBCs in CMAS environment can be attributed to the diffusion of molten silicates through the pores and micro-cracks of the ceramic top layer to the TBC and then release of the ZrO2 stabilizer and finally the tetragonal to monoclinic ZrO2 phase transformation. Keywords Thermal barrier coatings (TBCs) . ZrO2 9.5Y2O3 5.6Yb2O3 5.2Gd2O3 . 8YSZ . Calcium-magnesium-aluminosilicate . Hot corrosion
Introduction The ash cloud crisis was one of the major challenges of the European airlines in 2010 which resulted in the canceling of several flights and wondering of the passengers. Upon eruption of one of the most important volcanoes in Iceland (Eyjafjallajokull), European countries decided to close their airlines. The most important reason was the destruction in
* M. Bahamirian [email protected] 1
Department of Mining and Metallurgical Engineering, Yazd University, Yazd 89195-741, Iran
2
Department of Materials Engineering, University of Tarbiat Modares, Tehran, Iran
3
Department of Ceramics, Materials and Energy Research Center, Karaj, Iran
4
Faculty of Technology and Engineering, Department of Metallurgy and Materials Engineering, Shahrekord University, Shahrekord, Iran
the airplane engines due to the effect of the fine particles (smaller than 2 mm) in the volcano ash [1–3]. A huge volume of air can be sucked by airplanes’ engines during their operations. If the air contains ash particles (especially those rich in glass silicates), these particles will be molten in the temperature range of 1100–1500 °C and flow on the turbine blades (i.e., IN738LC). This phenomenon disturbs the balance in turbine blades and disrupts the engine motion [4, 5]
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