弥散贵金属微粒增韧复合热障涂层的结构与特性研究

In this project, new type thermal barrier coatings will be studied, in which, an Al2O3-YAG(Y3Al5O12) composite layer (AYTD) toughened by dispersed noble metal particles is used as the bonding coating, and thermal barrier layers (TBTD) (including double layers), such as YSZ、La2Zr2O7、LaTi2Al9O19 and YAG toughened by dispersed noble metal particles, are used as the top layers to insulate heat respectively. The key scientific issue in this study is the toughening mechanism on oxide ceramics doped with dispersed noble metal particles. Based on this fundamental research, the structure and characteristics of these composite TBCs will be studied, including: (a) the synergetic effect of both of dispersed noble metal particles and YAG particles on the improvement of enhancing the cohesion, cracking resistance, spalling resistance and high-temperature oxidation resistance of AYTD layer, and avoiding the reduction of mechanical properties of substrate alloy; (b) the mechanism for dispersed noble metal particles to enhance the properties, such as cohesion, cracking resistance, spalling resistance and the influence on insulating heat, of various TBTD layers. These new type thermal barrier coatings will be prepared by surface-applied composite slurry layers and micro-wave sintering combined with a compressed force. Under this researching works, new theory and techniques for the development of new type TBCs will be suggested. Therefore, this project can be considered as one with an important scientific value. It is confident that such composite TBCs toughened by dispersed noble metal particles have a wide potential application in the fields, such as aviation, spaceflight, communications and power resources, etc.

本项目提出研究以弥散贵金属微粒增韧的Al2O3-YAG(Y3Al5O12)复合层为抗氧化粘结层，以弥散贵金属微粒增韧的YSZ、La2Zr2O7、LaTi2Al9O19和YAG等热障陶瓷层（包括双热障陶瓷层）为隔热层构成的新型热障涂层。研究的关键科学问题是弥散贵金属微粒增韧氧化物陶瓷的机理。在此基础上，深入研究新型热障涂层的结构与特性的关系，包括：(a)弥散贵金属微粒和YAG微粒协同作用提高复合粘结层的结合力、抗开裂、抗剥落、抗高温氧化性能的机理，以及避免基体合金力学性能下降的机理；(b)弥散贵金属微粒提高各种热障陶瓷层的结合力、抗开裂、抗剥落、以及对隔热性能影响的机理。本项目将采用涂覆复合料浆层加压微波烧结技术，制备各种弥散贵金属微粒增韧的新型热障涂层。这些研究有望为热障涂层的发展提供新的理论和新的技术途径，因而具有重要的科学意义。展望未来弥散贵金属微粒增韧复合热障涂层具有广泛的应用前景。

热障涂层是发展先进航空发动机的关键技术。现有热障涂层的失效主要是由于涂层中各层材料的热膨胀系数差异导致的热应力不匹配所造成。本项目研究通过弥散贵金属微粒对热障涂层的增韧作用，使热障涂层能够承受较大的热应力而不发生失效，大幅度提高热障涂层的服役寿命。本项目的主要研究内容和相应的研究成果包括三个方面:一、通过测试电压-电流密度曲线，揭示了阴极表面形成气膜的状态与等离子放电的关系。采用在阴极区施加陶瓷微珠，在电解液中加入水溶性无极性高分子和溶胶约束阴极表面氢气的传输过程，显著减低等离子放电的电流密度，提高了等离子放电的均匀性，实现了在大面积复杂形状构件上沉积各种陶瓷涂层和弥散贵金属的复合陶瓷涂层。二、制备出弥散Pt微粒增韧的六种Al2O3-Pt、Al2O3-ZrO2-Pt、YAG-Al2O3- Pt、YSZ-Pt、ZrO2-Al2O3-Pt、La2Zr2O7-Pt单层热障涂层和二种YSZ-Pt/Al2O3-Pt、Al2O3-Pt/La2Zr2O7-Pt双层热障涂层。根据双层介电材料放电的Maxwell-Wagner 理论，建立了阴极等离子电解沉积陶瓷层的气膜/陶瓷膜双层放电机制。提出陶瓷层的导电性能决定双层放电的相对强度和涂层结构的，由此机制可以解释陶瓷涂层中弥散Pt微粒，涂层的孔隙率下降的现象。三、获得的弥散Pt微粒增韧的热障涂层具有优异的隔热性能，抗高温循环氧化和抗剥落性能。涂层的断裂韧性测试结果表明，弥散Pt微粒热障涂层的断裂韧性显著提高。证明了厚的Al2O3-Pt涂层由于弥散Pt微粒增韧的作用和微孔结构可以成为单层热障涂层；薄的Al2O3-Pt涂层可以作为粘结层替代传统MCrAlY或Pt改性铝化物的粘结层，构成Al2O3-Pt/La2Zr2O7-Pt双层热障涂层，提高抗高温循环氧化性能；薄的Al2O3-Pt涂层还可以作为热障涂层的外层，构成YSZ-Pt/Al2O3-Pt双层热障涂层，提高涂层的抗高温循环氧化和抗热腐蚀的性能。证明了弥散Pt微粒增韧的La2Zr2O7-Pt单层低膨胀系数的隔热陶瓷层可具有优异的抗高温循环氧化和抗剥落性能。提出了弥散Pt微粒的增韧热障涂层的机理：弥散Pt微粒通过塑性变形吸收裂纹扩展的能量；弥散Pt微粒使裂纹尖端钝化；大量弥散Pt微粒可以降低裂纹的长度。 本研究为制备新型热障涂层，提高热障涂层的性能提供了新的理论和新的技术途径。