| 溅射Ni3Al涂层改性及其高温氧化行为研究 | |
| 牛建民 | |
| Subtype | 博士 |
| Thesis Advisor | 王福会 ; 朱圣龙 |
| 2012 | |
| Degree Grantor | 中国科学院金属研究所 |
| Place of Conferral | 北京 |
| Degree Discipline | 腐蚀科学与防护 |
| Keyword | 磁控溅射 活性元素 铂 预氧化 氧化 Magnetron Sputtering Reactive Element Platinum Pre-oxidation Oxidation |
| Other Abstract | " 高温防护涂层应该兼具优良的高温氧化性能和基体相容性。传统涂层，如铝化物涂层、MCrAlY涂层等，通过提高涂层中的铝含量实现高温防护，当温度高于1100℃时，涂层与基体间的互扩散加快涂层退化，传统涂层无法满足高推比发动机叶片的防护要求。溅射高温合金纳米晶涂层成分与基体合金相近，在一定程度上减缓了涂层与基体之间的互扩散；铂改性g-Ni+g'-Ni3Al双相涂层抗氧化性能与传统的铂铝涂层相近，但是在涂层脆性、涂层与基体之间的互扩散方面，具有更为优异的基体相容性；在合金或涂层中添加适量的活性元素能够改变合金的氧化机制，促进保护性氧化膜的形成，显著提高氧化膜的粘附性；预氧化很重要的涂层处理工艺，而稀薄气氛则是普遍使用的处理手段。本论文通过预氧化处理、铂改性与添加活性元素对溅射纳米晶涂层进行改性，并针对涂层的高温氧化行为与机制进行了研究。 通过磁控溅射方法制备的Ni3(Al, Hf)纳米晶涂层具有柱状晶结构，为非稳态的超固溶g-Ni单相结构。在溅射纳米晶Ni3(Al, Hf)表面镀铂并进行扩散处理得到了与基体相结构相近的铂改性g'-Ni3(Al, Hf)单相涂层，不含Hf的涂层没有明显的浓度梯度，而含Hf的涂层中则有比较明显的浓度梯度，活性元素Hf阻碍了合金元素在其中的扩散；Pt促进了Al的上坡扩散，对Mo的扩散没有明显影响。 晶粒细化对Ni3Al中铝的选择性氧化没有明显影响，但是却阻止了氧化膜-涂层界面处空洞的形成。添加0.5 wt.%的Hf促进了铝的选择性氧化，降低了溅射Ni3Al纳米晶涂层稳态氧化阶段的氧化速率，并抑制了涂层中铝的贫化区的形成。当涂层中Hf的含量提高到2.0 wt.%时，则增加了涂层的氧化速率，促进了涂层中贫铝区的形成。活性元素Hf抑制了暂态Al2O3向稳态a-Al2O3的转变。Hf抑制了Al和Mo的扩散。 涂层中固溶态的铂促进了初期氧化时铝的选择性氧化，抑制了NiAl2O4的形成；铂降低了铝的活度，促进了铝的上坡扩散，减缓了由于氧化所导致的涂层中铝的消耗，抑制了涂层中贫铝区的形成；对于铂改性的溅射涂层，铂提高氧化膜粘附力的有益作用没有得到体现。当铂作为单质残留在氧化膜表面时，铂会对涂层的氧化起到催化作用，加快氧化反应速率。 预氧化处理工艺对涂层的氧化行为有重要的影响，适当的预氧化处理工艺大幅度提高了涂层的抗氧化性能。低氧分压促进了Al的选择性氧化，抑制了富Ni氧化物的形成；涂层表面形成的Al2O3膜经历非晶→暂态→稳态的发展过程；将氧分压对涂层成膜行为的影响绘成氧化物-氧分压图。 "; " Improving efficiency of aeroengine turbines involves raising the temperature of blade surface, but it is difficult for superalloys to simultaneously meet the performance of mechanics and oxidation resistance at high temperature, so protective coatings are often applied to the superalloys. For traditional coatings, the protection from high temperature oxidation is achieved by raising the concentration of Al in coatings, such as b-aluminide and MCrAlY coatings. However, serious inward diffusion of Al from coatings to substrates occurs, which results in depletion of Al in the protective coatings. Meanwhile, the formation of brittle phases in the interdiffusion zone resulted from the interdiffusion between coating and substrate reduces mechanical property of coating systems. As a result, the traditional coatings with high Al concentration are barely capable of meeting the needs of further improving efficiency of aeroengine turbines. The magnetron-sputtered nanocrystalline coating, with the same or similar chemical composition of superalloy substrates, prohibits or reduces the interdiffusion between coating and substrate during service at high temperature. Recent studies have indicated that the Pt-modified g-Ni+g′-Ni3Al coating exhibits excellent oxidation resistance, less interdiffusion and better compatibility between coating and superalloy substrate comparing to b-(Ni,Pt)Al coating. In the practice of engineering, preoxidation is an important method to improve oxidation resistance of coatings, and rarefied gas is usually applied to preoxidation of coatings. In the present work, preoxidation, Pt-modification and reactive element addition were applied to sputtered nanocrystalline coatings. The oxidation behaviors and mechanism of the coatings were investigated. The surface morphology and the fractured cross section of the sputtered Ni3(Al, Hf) films showed columnar microstructure and consisted of only supersaturated g-Ni phase. Subsequently, Pt-modified g'-Ni3(Al, Hf) single phase coatings were prepared by electroplating 1.5 mm thick layer of platinum on the sputtered Ni3(Al, Hf) film system with a following vacuum-annealing. There was no distinct gradient of chemical compositions in the Pt-modified sputtered coating without Hf while distinct gradient for that with Hf, which showed that Hf retarded diffusion of alloying elements. Presence of Pt resulted in uphill diffusion of Al from substrate to coating but had no distinct effect on diffusion of Mo. Nanocrystallization had little effect on selective oxidation of Al for Ni3Al alloy but prohibited the void formation at oxide-metal interface and enhanced the spallation resistance. Addition of 0.5wt.% Hf promoted the selective oxidation of Al, reduced the protective scale growth rate and retarded formation of Al-depleted zone in the coating. The increase in the Hf content to 2.0 wt.% in nanocrystalline Ni3Al coating actually promoted oxidation rate and the formation of Al-depleted zone in the coating. The addition of Hf retarded the q→a transformation of alumina and diffusion of Al and Mo. Presence of Pt in the coatings inhibited the formation of NiAl2O4 and promoted selective oxidation of Al in the early stage of oxidation. It was evident that the replenishment of Al from the substrate to the coating retarded the phase transformation from g′-Ni3Al to g-Ni in the Pt-modified coatings due to the growth of alumina scale. Therefore, the presence of Pt reduced Al consumption and inhibited the formation of Al-depleted zone in the coating, which was attributed to the rapid formation of alumina scale in the early stage of oxidation and Al up-hill diffusion from the substrate to the coating. Consequently, Pt had no beneficial effect on the adhesion between the oxide and the metal for the sputtered coatings. Oxidation rate was accelerated by catalyze effect of Pt as leftover particles on the surface of coatings. Pre-oxidation treatment processes had an extreme effect on oxidation behaviors. It was shown in the present work that appropriate treatment processes greatly enhanced resistance to oxidation coatings, and vice versa. Low oxygen partial pressure premoted selective oxidation of Al and inhibited formation of Ni-enriched oxides. Alumina formed on the surface of coatings underwent the course: amorphous state→transient state→steady state. Accordingly, oxide-oxygen partial pressure map was drawn based on the results. " |
| Document Type | 学位论文 |
| Identifier | http://ir.imr.ac.cn/handle/321006/64497 |
| Collection | 中国科学院金属研究所 |
| Recommended Citation GB/T 7714 | 牛建民. 溅射Ni3Al涂层改性及其高温氧化行为研究[D]. 北京. 中国科学院金属研究所,2012. |
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