| LI Meng-qi,PENG Hui,WEN Jiao,GUO Hong-bo.Oxidation Resistance of HY3 Coating Deposited by Arc Ion Plating with Powder Metallurgy Target[J],52(6):276-284, 360 |
| Oxidation Resistance of HY3 Coating Deposited by Arc Ion Plating with Powder Metallurgy Target |
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| DOI：10.16490/j.cnki.issn.1001-3660.2023.06.024 |
| KeyWord:arc ion plating high temperature protective coating MCrAlY oxidation resistance microstructure |
| Author | Institution |
| LI Meng-qi |
Research Institute for Frontier Science,Beijing , China |
| PENG Hui |
Research Institute for Frontier Science,Beijing , China ;Ministry of Industry and Information Technology Key Laboratory of High-temperature Structural Materials and Coating Technology, Beijing , China |
| WEN Jiao |
School of Materials Science and Engineering, Beihang University, Beijing , China |
| GUO Hong-bo |
School of Materials Science and Engineering, Beihang University, Beijing , China;Ministry of Industry and Information Technology Key Laboratory of High-temperature Structural Materials and Coating Technology, Beijing , China |
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| Abstract: |
| MCrAlY coatings are commonly used to protect turbine blades against hot temperature attack. This work aims to investigate the effect of target preparation methods on the oxidation behavior of MCrAlY coatings fabricated by arc ion plating (AIP). NiCrAlYSi (HY3) targets prepared by powder metallurgy (PM) were used as raw material, and HY3 coatings were deposited on DZ125 substrates by AIP (denoted as P coating). Coating specimens were also deposited with casting target for comparison (denoted as C coating). Vacuum annealing was carried out at 960 ℃ for 3 h to promote homogenization of the coatings subsequently. Microstructure of both targets and coatings before and after oxidation were analyzed with scanning electron microscope (SEM) equipped with energy spectrometer (EDS) and X-ray diffractometer (XRD). Isothermal oxidation tests were performed at 1 100 ℃ for 200 h. Then oxidation curves were obtained by plotting weight gains of coatings against oxidation time. Thermal grown oxide (TGO) formed after short-term oxidation (10 min) was analyzed by photo-stimulated luminescence spectra to reveal the possible mechanism. The results showed that the PM targets exhibited much smaller phase size of about 5 μm, almost one order of magnitude lower than that of C target. Both coatings in annealed condition were uniform and dense, with a similar thickness of about 30 μm, mainly composed of γʹ and β phases. However, results analyzed with Image J (an image processing software) indicated that the volume fraction of β phase precipitated in the P coating was about 64%, which was significantly higher than the value of about 45% detected in the C coating. The finer microstructure of the P target resulted in the uniform distribution of Al in the coating, thus was responsible for the higher volume fraction of β phase. The mass gain values of P and C coatings after 200 h oxidation were about 1.01 mg/cm2 and 1.10 mg/cm2, respectively. The mass gain values for the coatings were close to each other, but obvious spallation of TGO could be observed for the C coating. No peeling or spallation of oxides occurred to the P coating. Cross-sectional examination of coatings after 200 h oxidation demonstrated that the thickness of TGO grown on P coating was about 3.9 μm, with a small amount of Y2Hf2O7 dispersion. TGO formed on the C coating was about 4.5 μm thick, which was slightly thicker than that of the P coating. Pegs with larger size in the TGO of C coating were determined as HfO2. Similar to the aluminum distribution behavior, homogeneous yttrium in the P coating resulted in the formation of finely dispersed Y2Hf2O7 pegs in TGO, which improved the scale spallation resistance. As a comparison, larger HfO2 pegs could be observed in the oxidized C coating, as a result of the more severe segregation of yttrium and hafnium. The 10 min short-term oxidation test indicated that the TGO developed on the P coating contained α-Al2O3 and a small amount of θ-Al2O3, which was different from the TGO of C coating with completely transformed α-Al2O3. The retarded transformation of θ to α-Al2O3 can be attributed to the higher volume fraction of β phase in the P coating. Nucleation of θ-Al2O3 is promoted by the rapid outward diffusion of Al along the γʹ/β phase boundaries at the initial stage of oxidation, which transforms into a more protective α-Al2O3 subsequently. Consequently, the P coating reveals improves oxidation and scale spallation resistance than the C coating in isothermal oxidation tests performed at 1 100 ℃. |
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