| LIU Lu,LIU Ya,WU Changjun,WU Yufeng,SU Xuping.Effect of Pre-oxidation Treatment on High Temperature Oxidation Behavior of MP35N Alloy[J],53(2):60-70 |
| Effect of Pre-oxidation Treatment on High Temperature Oxidation Behavior of MP35N Alloy |
| Received:November 15, 2022 Revised:May 09, 2023 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.02.005 |
| KeyWord:MP35N Co-Ni-20Cr alloy pre-oxidation Al2O3 oxide film oxidation mechanism surface modification |
| Author | Institution |
| LIU Lu |
Jiangsu Key Laboratory of Materials Surface Science and Technology, Jiangsu Changzhou , China |
| LIU Ya |
Jiangsu Key Laboratory of Materials Surface Science and Technology, Jiangsu Changzhou , China;Jiangsu Collaborative Innovation Center of Photovoltaic Science and Engineering, Changzhou University, Jiangsu Changzhou , China |
| WU Changjun |
Jiangsu Key Laboratory of Materials Surface Science and Technology, Jiangsu Changzhou , China |
| WU Yufeng |
Jiangsu Key Laboratory of Materials Surface Science and Technology, Jiangsu Changzhou , China |
| SU Xuping |
Jiangsu Key Laboratory of Materials Surface Science and Technology, Jiangsu Changzhou , China;Jiangsu Collaborative Innovation Center of Photovoltaic Science and Engineering, Changzhou University, Jiangsu Changzhou , China |
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| Abstract: |
| In order to prepare the pre-oxidation film with good high temperature oxidation resistance, the nonconsumable vacuum arc furnace was used to melt the alloy, and the alloy samples were cut into 10 mm×10 mm×1 mm thin sheets for pre-grinding and polishing after annealing at 1 000 ℃ in the box furnace for 7 days. The Rhine apparatus was used for pre-oxidation experiment. The balanced oxygen pressure was obtained by heating metal and its oxide powder in a vacuum container. The oxygen pressure in the quartz tube was 1.9×10–3 Pa, and then heat treatment was conducted in a double temperature tube furnace. The effect of Si element on the activity of Al element was calculated by pandat software. The alloy structure phase diagram and oxidation phase diagram of Co-Ni-Cr-Mo-Al-Si system were calculated by FactSage software. The morphology, chemical composition and element distribution of the oxidation film surface and section of the pre-oxidation sample were characterized and the phase was analyzed by X-ray diffraction and scanning electron microscope. At 1 000 ℃ under oxygen pressure of 10–17 atm oxygen pressure, Cr2O3 oxide appeared on the surface of MP35N alloy without Si. With the increase of Si addition in the alloy, the surface oxide of the alloy became (Al,Cr)2O3, mainly composed of Cr2O3 oxide, and the internal oxide was Al2O3. When the content was 3%, a nearly continuous band-shaped Al2O3 oxide film was formed inside. Under the oxygen pressure of 10–25 atm, continuous Al2O3 film was formed on the alloy surface. Under the oxygen pressure of 10–17 atm, the outer oxide film of the Co-Ni-20Cr-10Mo-4Al-1Si alloy after pre-oxidation was Cr2O3, and the inner oxide was Al2O3. With the increase of oxygen pressure, spinel phase oxides were formed on the surface in the air. After pre-oxidation for 1 h, 5 h and 10 h at 1 000 ℃ and 10–17 atm oxygen pressure, the external oxide film on the surface of Co-Ni-20Cr-10Mo-4Al-1Si alloy was Cr2O3, and the internal oxide was Al2O3. With the extension of time, the coarse Cr2O3 particles on the surface transformed into dense Cr2O3 oxide film. Al2O3 gradually became continuous from the acicular oxide at the initial stage of oxidation and the oxide layer became thicker. When the pre-oxidation time was extended to 20 h, the outer layer of Cr2O3 film completely peeled off, and the alloy surface formed a continuous external oxidation Al2O3 film. The Si-containing alloys formed an additional SiO2 layer at the scale-alloy interface, effectively reducing Cr2O3 growth rate and Cr depletion in the underlying alloy. With the increase of Si addition, the activity of Al element increased continuously, which promoted the formation driving force of Al2O3 and the diffusion coefficient of Al element, and more Al element diffused to the surface of the alloy. At the same time, the addition of Si promoted the nucleation of metastable and stable alumina, which contributed to the selective oxidation of aluminum, so that continuous metastable and stable alumina oxide scales could be rapidly formed. At the same time, stable Al2O3 precipitation was formed at the interface of internal oxidation alloy, which slowed down the development of external nickel rich layer. The reduction of pre-oxidation oxygen pressure and the extension of oxidation time are conducive to the formation of protective external oxidation Al2O3 film, which can effectively improve the high temperature oxidation resistance and corrosion resistance of the alloy. |
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