| TAN Xiaoxiao,WU Ziwen,SUN Dan.High Temperature Oxidation Behavior of Nano-Al2O3 Modified β-NiAl Coating[J],53(24):79-87 |
| High Temperature Oxidation Behavior of Nano-Al2O3 Modified β-NiAl Coating |
| Received:December 29, 2023 Revised:July 08, 2024 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.24.007 |
| KeyWord:aluminide coating electroplating annealing interdiffusion oxidation nanoparticles |
| Author | Institution |
| TAN Xiaoxiao |
Engineering Training Center,Shanghai , China ;School of Materials Science and Engineering, Shanghai University of Engineering Science, Shanghai , China |
| WU Ziwen |
School of Materials Science and Engineering, Shanghai University of Engineering Science, Shanghai , China |
| SUN Dan |
School of Materials Science and Engineering, Shanghai University of Engineering Science, Shanghai , China |
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| Abstract: |
| To improve the high temperature oxidation behavior of the aluminide coating, nano-Al2O3 particles were added and uniformly dispersed in the coating. Al2O3-modified and Al2O3-free δ-Ni2Al3 coating systems were prepared by aluminizing electroplated Ni-Al2O3 and Ni films on Ni substrates at 620 ℃. Accordingly, the two δ-Ni2Al3 coating systems were vacuum annealed at 1 000 ℃ for 10 min to obtain Al2O3-modified and Al2O3-free β-NiAl coating systems. Then, these two β-NiAl coating systems were oxidized at 1 000 ℃ for 20 h. The structures and morphologies of these aluminide coatings before and after oxidation were observed through X-ray diffraction (XRD) and scanning electron microscopy (SEM)/energy dispersive spectroscopy (EDS) analysis. After 10 minutes of vacuum annealing at 1 000 ℃, the Al2O3-modified δ-Ni2Al3 coating system degraded to Al rich β-NiAl phases at the depth of XRD detection, while the Al2O3-free coating degraded to Ni rich β-NiAl phases. The cross-sectional morphologies of these two coatings were consistent with the XRD results. The oxidation kinetics curves of the modified and unmodified β-NiAl coating systems at 1 000 ℃ showed that the overall oxidation weight gain of the coating decreased after the addition of nano-Al2O3 particles. According to the difference in oxidation rates, the oxidation process of these two coatings could be divided into two stages:stage Ⅰ with a fast oxidation rate and stage Ⅱ with a slow oxidation rate. There was not much difference in the oxidation rate between these two coatings after entering stage Ⅱ. It was found that the oxidation rate of stage Ⅰ for the Al2O3-modified coating was relatively high compared to the Al2O3-free coating. However, the transition time from stage Ⅰ to stage Ⅱ occurred earlier for the Al2O3-modified coating. Once the oxidation process entered stage Ⅱ, the oxidation rate significantly decreased. After 20 h of oxidation, the oxide scales on surfaces of both coatings were α-Al2O3. The Al2O3-modified coating degraded to Ni rich β-NiAl and γ′-Ni3Al phases, while the unmodified coating completely degraded to γ′-Ni3Al phases within the range detected by XRD. The results showed that the degradation of the coating was reduced after the addition of nano-Al2O3 particles. From the cross-sectional morphology of the Al2O3-modified coating, it was observed that the oxide scale of the modified coating was dense and well-bonded to the substrate after oxidation. Meanwhile, some small-sized cavities were found at the oxide scale/coating interface and inside the coating.However, the surface of the unmodified coating exhibited significant spallation after oxidation and large-sized cavities were found in the spallation area. Cavities exceeding 5 μm also presented at the oxide scale/coating interface where the oxide scale had not peeled off. These observations indicated that the adhesion of the oxide scale was improved after modification with nano-Al2O3 particles. The results above show that the addition of the nano Al2O3 particles can reduce the oxidation rate and increase the oxide adhesion of the aluminide coating, resulting in a lighter degradation of the Al2O3-modified coating under the same oxidation conditions. |
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