不同显微结构 Yb2Si2O7 环境障涂层的抗热震性能研究

采用低压等离子喷涂工艺 (LPPS) 在 SiCf/SiC 复合材料表面依次制备了 Si 底层、 Mullite 中间层和 Yb2Si2O7 面层的环境障涂层。 通过不同的喷涂参数分别制备出层状结构和层柱混合结构的 Yb2Si2O7 面层， 并考察面层结构 对环境障涂层抗热震性能的影响。 结果表明， 所制备的两种面层涂层均具有孔隙率低、 界面结合紧密的特点， 层柱 混合结构的面层中柱状结构为 Yb2Si2O7 气化所形成， 而层状结构为液相沉积所形成。 X 射线衍射分析结果显示， 层状涂层结晶良好， 而层柱混合结构涂层中存在大量的非晶态。 对非晶态进行热处理可得到结晶完全的层柱混合 结构涂层。 热震实验结果表明， 层状涂层经 355 次热震后脱落面积很小， 表现出良好的抗热震性能。 相比之下， 非晶态层柱混合结构涂层经热震 3 次后即出现脱落， 经 155 次热震后脱落面积达到 5%， 抗热震性能较差。 晶态 的层柱混合结构涂层经热震 20 次后出现脱落， 随后脱落速度减缓， 但到第 40 次热震时， 涂层大块脱落加速失效。

Research on Thermal Shock Resistance of Yb2Si2O7 Environmental Barrier Coatings with Different Microstructures

The environmental barrier coatings of Si (bottom layer), Mullite (middle layer), and Yb2Si2O7 (surface layer) were sequentially prepared on the surface of SiCf/SiC composites by low-pressure plasma spraying process (LPPS). Two types of Yb2Si2O7 surface layers with layered structure and layer-column mixed structure were deposited via adjusting spraying parameters. The effects of Yb2Si2O7 microstructure on thermal shock resistance of the environmental barrier coatings were investigated. The results showed that both the Yb2Si2O7 coatings prepared by LPPS exhibited low porosity and tight interface bonding. The columnar structure in the surface layer of the layer-column mixed structure is formed by Yb2Si2O7 gasification, and the layered structure is formed by liquid deposition. X-ray diffraction analysis results showed that the layered coating had good crystallization, while a large amount of amorphous state existed in the layer-column mixed structure coating, which can be heat-treated to obtain a fully crystalline coating. The thermal shock test results showed that the layered coating has a small shedding area after 355 thermal shocks, showing good thermal shock resistance. In contrast, the amorphous layercolumn hybrid structure coating appeared to fall off after 3 thermal shocks, and the fall-off area reached 5% after 155 thermal shocks, which meant that the thermal shock resistance was poor. The crystalline layer-column hybrid structure coating appeared to fall off after 20 thermal shocks, and then the rate of fall off slowed down, but by the 40th thermal shock, the coating fell off in large chunks and accelerated to failure.