稀土A、B位复合掺杂对锆酸镧热障涂层结构和热物理性能的协同影响规律及机理

Thermal barrier coatings (TBCs) has become one of the key technology for developing high performance aeroengine.The major role of the TBCs is to reduce the temperature of the metallic components and thereby to enhance component life and performance. Consequently, it is great significant to decrease the thermal conductivity of the TBCs. Lanthanum zirconate (La2Zr2O7) with a pyrochlore structure has been considered as the most promising candidate for the next generation of thermal barrier coatings, because it exhibits high melting point, high chemical stability and lower thermal conductivity. The glass-like thermal conductivity has been suggested in Y3+, Yb3+ or Er3+ doped La2Zr2O7 ceramic, however, the thermal expansion coefficient of the La2Zr2O7 ceramic has not been improved. Based on this, the Y3+, Yb3+ or Er3+ ions are selected to substitute the La3+ ion in the A-site and the Ce4+ ion is to partially substitute for the Zr4+ ion in the B-site, the synergistic effect of rare earth cations multi-doping on the structure and thermal conductivity will be studied and the reason for the low thermal conductivity found in this system will be discussed. The influence of different technological parameters of EB-PVD on the microstructure and thermal properties of the coatings will be investigated . The relation between the existence of rattlers and the substituting species of cations and the influence of various substituting cations on the glass-like thermal conductivity for this system will be revealed, which provides a way to further reduce thermal conductivity and improve the microstructure and thermal properties of thermal barrier coatings.

热障涂层已成为发展高性能航空发动机的关键技术之一，其主要目的是降低金属基体的温度，从而提高航空发动机的性能和寿命。因此，探索进一步降低热障涂层材料热导率的途径具有重要意义。锆酸镧具有高熔点、良好的高温稳定性和低热导率，被认为是最具希望的下一代热障涂层材料之一。Y3+、 Yb3+或Er3+离子A位掺杂的La2Zr2O7体系呈现出玻璃化导热行为，但其热膨胀系数并未得到明显提高。基于此，本项目将探索Y3+、Yb3+、Er3+等稀土离子A位和Ce4+离子B位复合掺杂降低锆酸镧热导率的途径，研究稀土离子复合掺杂对材料结构和热导率的协同影响规律及机理；研究EB-PVD不同工艺参数对涂层组织结构及热性能的影响规律；得出掺杂剂对烧绿石结构材料中“rattlers”存在状态，进而得出对材料的玻璃化导热行为的影响规律，为探索进一步降低该体系热障涂层材料热导率的途径提供思路，进而获得改善涂层结构和热性能的方法。

本项目利用固相法1600℃高温合成了A、B（A=Gd，Y，Er等，B=Ce ，Ti，Nb等）位掺杂La2Zr2O7和Gd2Zr2O7陶瓷材料，分析A、B位离子掺杂对陶瓷材料结构及热物理性能的影响。结果表明，A、B位离子掺杂La2Zr2O7和Gd2Zr2O7的陶瓷均为单一烧绿石或缺陷型萤石结构，陶瓷材料的微观形貌致密且晶界清晰，晶粒尺寸5μm左右，元素均匀分布无偏析。A、B位离子掺杂后，La2Zr2O7陶瓷热膨胀系数提高1.0×10-6 K-1以上，热导率显著降低；Gd2Zr2O7陶瓷的热膨胀系数达到11.05×10-6 K-1左右，热导率在600℃以下有效降低，600℃以上与未掺杂试样接近。机理研究表明，室温-600℃，A、B位离子掺杂陶瓷材料热导率降低的机制是声子-点缺陷散射、“rattlers”-散射和高熵效应协同作用；而800℃以上热导率出现升高则是由高温热辐射所引起。.采用EB-PVD工艺制备了A、B位离子掺杂La2Zr2O7热障涂层，确定了沉积工艺参数，探讨涂层的组织结构，评价了涂层的性能。结果表明，转速对柱状晶的生长形貌有显著影响，在非0转速下柱状晶的生长具有统计方向一致性，，转速提高后，涂层循环寿命逐渐降低。860-880℃，转速为5r/min下沉积涂层的热循环寿命至少为100小时。Y，Gd和Ce的共掺杂使La2Zr2O7涂层表现出良好的热物理性能、热循环性能，但随掺杂量的进一步增加，会使涂层热循环及热冲击寿命有所降低。