| WANG Da-wang,LI Qi-lian,ZHANG Le,LI Shu-qing,YANG Wei-hua.Microstructure and Resistance to Molten Salt Corrosion of Si-Yb2O3/Yb2Si2O7/Yb2SiO5 EBC[J],52(5):131-139, 162 |
| Microstructure and Resistance to Molten Salt Corrosion of Si-Yb2O3/Yb2Si2O7/Yb2SiO5 EBC |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.05.013 |
| KeyWord:environmental barrier coatings vacuum plasma spray rare earth silicate molten salt corrosion high temperature oxidation |
| Author | Institution |
| WANG Da-wang |
AVIC Manufacturing Technology Institute, Beijing , China;Science and Technology on Power Beam Processes Laboratory, Beijing , China;Aviation Key Laboratory of Science and Technology on Advanced Surface Engineering, Beijing , China |
| LI Qi-lian |
AVIC Manufacturing Technology Institute, Beijing , China;Science and Technology on Power Beam Processes Laboratory, Beijing , China;Aviation Key Laboratory of Science and Technology on Advanced Surface Engineering, Beijing , China |
| ZHANG Le |
AVIC Manufacturing Technology Institute, Beijing , China;Aviation Key Laboratory of Science and Technology on Advanced Surface Engineering, Beijing , China |
| LI Shu-qing |
AVIC Manufacturing Technology Institute, Beijing , China;Science and Technology on Power Beam Processes Laboratory, Beijing , China;Aviation Key Laboratory of Science and Technology on Advanced Surface Engineering, Beijing , China |
| YANG Wei-hua |
AVIC Manufacturing Technology Institute, Beijing , China;Science and Technology on Power Beam Processes Laboratory, Beijing , China;Aviation Key Laboratory of Science and Technology on Advanced Surface Engineering, Beijing , China |
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| Abstract: |
| SiCf/SiC composite materials have high specific strength, high specific modulus and other excellent mechanical properties at high temperature. SiCf/SiC composites have excellent oxidation resistance due to the reaction with oxygen in the air to form a dense layer of SiO2 protective film. However, molten salts from the environment dissolve the SiO2 protective film, resulting in rapid corrosion of SiCf/SiC composites. The most common molten salt impurities in aero-engine combustion chambers, turbines, and tail nozzle environments are molten Na2SO4 and NaCl. Environmental barrier coatings (EBCs) are generally used to resist oxidation and corrosion of composite materials by the gas environment. Plasma spraying technology is the most important EBC preparation technology, which has the characteristics of fast deposition rate, high production efficiency, strong adaptability to specimen shape and size, and large controllable range of coating thickness. A three-layer EBC was prepared by vacuum plasma spraying process, the EBC with rare earth Yb2O3 doped Si as the bottom layer, Yb2Si2O7 as the middle layer, and Yb2SiO5 as the surface layer. The three-layer structure EBC was investigated at 900 ℃. The corrosion behavior of molten salt was researched in an environment mixed with NaCl and Na2SO4 at a mass ratio of 1∶1. The Si-Yb2O3/Yb2Si2O7/Yb2SiO5 three-layer structure EBC was prepared on one side of the sample surface by vacuum plasma spraying process. Continuous 100 h molten salt corrosion test was carried out in +50wt.% Na2SO4 mixed salt. Optical microscope, scanning electron microscope and X-ray diffractometer were used to observe and test the morphology of the three-layer EBC before and after molten salt corrosion, analyze its structure and chemical reaction mechanism in the molten salt corrosion process. After continuous molten salt corrosion at 900 ℃ for 100 h, the matrix SiCf/SiC composite was completely corroded; the bottom layer Si and Yb2O3 were partially missing and the coating was incomplete; the intermediate layer Yb2Si2O7 formed a large number of holes after molten salt corrosion. However, the original coating frame size was still basically maintained; the thickness of the surface layer Yb2SiO5 was basically the same as that before the molten salt corrosion. After the molten salt corrosion, the structure was dense and its own chemical stability was maintained. The test results showed that since the EBC was prepared on one side of the SiCf/SiC substrate, and the SiC on the other side was completely exposed to molten salt. After molten salt corrosion, the substrate SiC was completely corroded, indicating that SiC itself did not have the ability to resist molten salt corrosion. After 100 h of molten salt corrosion in 50wt.%NaCl+50wt.%Na2SO4 mixed salt at 900 ℃, a large number of holes were formed in the Yb2Si2O7 interlayer, indicating that the molten salt was immersed in the interlayer during the corrosion, but its chemical stability was still basically maintained. The original coating frame size shows that the Yb2Si2O7 intermediate layer has certain anti-corrosion properties of molten salts. After 100 h molten salt corrosion in 50wt.% NaCl+50wt.%Na2SO4 mixed salt at 900 ℃, the thickness and size of Yb2SiO5 surface layer in EBC coating system are basically the same as before molten salt corrosion, the structure is compact, and its chemical stability is maintained, with good resistance to molten salt corrosion. SiCf/SiC composites have no resistance to molten salt corrosion. The underlying Si and Yb2O3 coatings have poor resistance to molten salt corrosion. In the system, the YB2Si2O7 interlayer has certain resistance to molten salt corrosion, while the Yb2SiO5 surface layer has good resistance to molten salt corrosion. Therefore, in the three-layer EBC coating system of Si–Yb2O3/Yb2Si2O7/Yb2SiO5, the order of molten salt corrosion resistance from low to high is:the bottom layer Si and Yb2O3 < interlayer YB2Si2O7 < surface layer Yb2SiO5. The EBC of this system has high molten salt corrosion resistance. |
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