Cf/SiC复合材料表面稀土复合氧化物高温热防护涂层研究

Cf/SiC composites are susceptible to ablation and oxidation in high-temperature oxidizing environment, and it has been proven that the coating protection is a better approach to improve the oxidation and ablation resistance of Cf/SiC composites. With the development of modern hypersonic weapons, it is desired that the coating could endure a flame with temperature up to 2273K and protect Cf/SiC from degredation by the flame. In this project, the novel coatings based on rare-earth oxides composites are designed and deposited on Cf/SiC substrate by atmospheric plasma spraying, which is believed to provide a good protection for the Cf/SiC substrate against the flame. The thermal stability at high temperature between rare-earth element silicates and thermal barrier ceramics of RMA with the plate-like strucutre will be studied. Effect of plasma spraying parameters on the microscopic defects and residual stress in the produced coatings will be explored. The oxidation and ablation protection behaviors of the coatings with the different designed structures for the Cf/SiC substrate will be investigated. Effect of the thermal stress kinetics factors on the formation and growth of defects in the coating will be analyzied. From these studies, the physical and chemical compatibility law between RMA and rare-earth element silicates at high temperature will be revealed, so is the regulation kinetics of microstructure, deposition defects and interfacial strength of the coatings. The kinetic behavior of oxidation and ablation protection, thermal protection mechanism and failure mechanism of the coatings based on the rare-earth oxides composites will be proposed. It is expected that this project could provide the valuable theoretical basis for the development of rare-earth oxides composites coatings and the corresponding preparation technology for Cf/SiC substrate as well as for the breakthrough of bottleneck of the high temperature thermal protection required by the new generation of hypersonic weapons for the Cf/SiC composites.

Cf/SiC抗氧化抗烧蚀性能较差，涂层防护是克服Cf/SiC性能不足的有效途径。现代超音速武器装备发展要求Cf/SiC表面涂层能够经受2273K火焰灼烧并对基底提供良好的热防护。本项目设计了新型稀土复合氧化物涂层，通过等离子喷涂技术制备涂层，有效地解决Cf/SiC在2273K火焰灼烧时的热防护难题。研究稀土硅酸盐和片状晶稀土热障陶瓷RMA的高温热稳定性、喷涂参数对涂层微观缺陷与残余应力的影响、不同结构涂层对Cf/SiC的抗氧化抗烧蚀行为和热应力动力学影响因素对涂层缺陷形成与生长的影响，揭示稀土硅酸盐与RMA高温物理化学相容性规律，揭示涂层微观组织、沉积缺陷和界面结合调控动力学规律，揭示稀土复合氧化物涂层对Cf/SiC的抗氧化抗烧蚀动力学行为与保护机理以及涂层失效机理，为发展Cf/SiC表面稀土复合氧化物涂层与制备技术和突破新一代高超音速武器装备对Cf/SiC高温热防护需求瓶颈奠定理论基础。

Cf/SiC在武器装备热端构件的应用瓶颈是抗氧化性能差。本项目研制了稀土复合氧化物涂层，解决了Cf/SiC在2273K火焰灼烧和1673K电炉加热下的热循环抗氧化难题。研究了稀土硅酸盐、铝酸盐粉末合成与表征、涂层成分与结构设计、涂层微观组织以及涂层热循环抗氧化行为与失效机理，为发展高温抗氧化涂层技术和突破武器装备对Cf/SiC热防护需求瓶颈奠定了理论基础。.采用固相反应合成了R2SiO5和R2Si2O7(R=Y,Er,Yb)粉末，发现Yb2SiO5和Yb2Si2O7粉末高温热稳定性较好。在R2Si2O7与LMA层之间设计R2SiO5层，不仅缓解了陶瓷层热膨胀不匹配，同时解决了R2Si2O7/LMA界面化学相容性差的问题。采用大气等离子喷涂制备了R2SiO5和R2Si2O7单陶瓷层、R2SiO5/LMA和R2Si2O7/LMA双陶瓷层、R2Si2O7/R2SiO5/LMA多陶瓷层以及R2Si2O7/**/LMA界面梯度结构涂层。涂层分布均匀，与基体结合良好。LMA面层提高了硅酸盐的热稳定性，双层结构抗氧化性能优于单层结构，多层结构抗氧化性能最好。.基体的孔隙和裂纹对涂层抗氧化性能影响显著，采用Si层是解决涂层抗氧化性能受控于基体缺陷的良好途径。基体本身的孔洞和裂纹是导致样品失重的主要原因。1673K电炉热循环15次共加热90min，Yb2Si2O7/LMA双层、Yb2Si2O7/Yb2SiO5/LMA多层、Yb2Si2O7/**/LMA梯度结构涂层样品失重率分别为4.9%，4.1%和5.3%，无涂层样品失重率36.5%；2273K火焰循环灼烧10次+连续灼烧25min共灼烧85min，Yb2SiO5/LMA单面涂层样品失重率为4.1%，无涂层样品失重率20.6%。发现陶瓷层厚度对抗氧化性能影响很大，硅酸盐层厚度尤其显著，涂层总厚度不应超过200微米。.揭示了涂层抗氧化失效机理:在热循环过程中，热膨胀不匹配应力和Si层氧化、硅酸盐烧结及其与铝酸盐界面反应产生的时效应力，诱导涂层出现裂纹，空气通过裂纹扩散，对基体表面氧化，基体氧化也加速了涂层开裂与脱落。抗氧化和热腐蚀失效研究表明涂层适合在短时间内（如几十分钟）对Cf/SiC提供良好的热防护。.通过涂层结构与成分设计，可显著优化稀土复合氧化物涂层的热防护性能，该涂层体系是现代超音速Cf/SiC热端构件短期热防护的发展方向。