单晶高温合金的纳米晶涂层中纳米结构与活性元素对高温氧化的协同作用机制研究

The high-density defects in nanocrystalline structure promote selective oxidation of Al and the fast formation of dense and intact Al2O3 scale, which provides a high resistance against high-temperature oxidation for alloys. Nanocrystalline coatings with the same chemical composition to the alloy substrates are prepared inheriting these merits. Besides, they avoid the problem of element inter-diffusion that traditional metallic coatings have suffered a lot, and thus have almost no harmful effect on microstructure and mechanical properties of the alloy substrate during their service at high temperature. On this account, nanocrystallite coating is of a special value for scientific research and shows great potential for application. Single-crystal superalloy contains a large amount of Ta which not only has demonstrated beneficial to the mechanical properties of alloys but also affects a lot on oxidation of alloy or its nanocrystalline coating, showing similar effects of reactive elements. Once minor amount of reactive element of Y is incorporated in its nanocrystalline coating, there exist synergistic effects between Y and Ta, Y and the nanocrystalline structure on oxidation. However, there is no systematical research on these unique phenomena by now. It is of especial urgency to establish the underlying mechanisms about these. In this project, nanocrystalline coatings with different Ta and Y contents will be prepared on single-crystal superalloys. The synergistic effects between nanocrystalline structure and Ta, nanocrystalline structure and Y, reactive element Y and Ta are researched, respectively. At last, the mechanisms of synergistic effect between nanocrystalline structure, reactive element Y and Ta are established, which provide guidelines for designing novel single-crystal superalloys as well as their nanocrystallline coatings

纳米晶结构的高密度缺陷能够促进铝的选择性氧化，快速形成致密完整的氧化铝膜，为合金提供优异的抗高温氧化性能。利用该特点制备的与合金基体同成分的纳米晶涂层，还可避免传统金属涂层所遇到的界面互扩散问题，服役过程中不影响基体合金的组织结构及力学性能，具有独特的科学研究价值和重要的应用前景。单晶高温合金中钽含量高，它除了有益于合金的力学性能外，还明显地影响了合金及其纳米晶涂层的氧化行为，表现出“类活性元素”效应。在涂层中进一步添加微量活性元素钇后，发现纳米晶涂层的高温氧化受到了钇与钽、钇与纳米结构的协同作用影响。而当前国内外尚无涉及这些独特现象的深入研究和报道，其内在机制更是亟需澄清。本项目拟溅射钽、钇含量不同的单晶高温合金纳米晶涂层，分别研究氧化过程中纳米晶结构与钽、纳米晶结构与钇以及钇与钽之间的协同作用，揭示纳米晶结构与钇、钽三者间的协同作用机制，为单晶高温合金及其纳米晶涂层的设计提供理论指导

纳米晶结构可促进铝的选择性氧化，为合金提供优异的抗高温氧化性能。利用该特点制备的与合金基体同成分的纳米晶涂层，还可避免传统金属涂层所遇到的界面互扩散问题，服役过程中不影响基体合金的组织结构及力学性能，具有独特的科学研究价值和重要的应用前景。单晶高温合金中钽含量高，明显地影响了合金及其纳米晶涂层的氧化行为，表现出“类活性元素”效应。在涂层中进一步添加微量活性元素钇后，发现纳米晶涂层的高温氧化受到了钇与钽、钇与纳米结构的协同作用影响。而当前国内外尚无涉及这些独特现象的深入研究和报道。通过本项目的研究，揭示了表面纳米晶结构与合金中固有的“活性元素”Ta、纳米晶结构与微量添加的活性元素Y以及活性元素Y与Ta之间的相互作用规律，阐明了表面纳米晶结构与活性元素间的协同作用机制，为新型的活性元素改性纳米晶涂层的设计与开发提供了理论指导。.通过该项目的资助，在纳米晶涂层高温防护机理研究的基础之上，掌握了单晶合金用活性元素改性纳米晶涂层的设计原理，并与中航发黎明公司合作，开展了发动机工况下纳米晶涂层的性能模拟研究。项目执行四年时间内，发表了SCI收录论文共21篇，培养博士毕业研究生3名，在读博士生1名。