电子束沉积SiC/ZrO2热防护层的结构优化及其抗热震性能

高性能辐射热防护层是高超声速飞行器金属热防护系统的重要组成部分。为获得高性能的热防护层,利用L5 EB-PVD电子束物理气相沉积设备在Haynes 214镍基合金表面沉积了SiC/ZrO2防护层,测试了其在热循环条件下的抗热震性能;通过分析其沉积温度及厚度对残余热应力的影响,确定了热防护层的沉积工艺参数。结果表明:热防护层在800℃和900℃循环80次后未出现明显的宏观裂纹;1000℃循环60次后,SiC表面层应力集中区出现裂纹,在交变热应力作用下,裂纹不断扩展形成网状龟裂纹,最终导致热防护层剥落;热膨胀系数不匹配导致热防护层在急冷急热热震过程中产生热应力是导致其失效的主要原因。

Structure Optimization of SiC/ZrO2 Thermal Protective Coatings Deposited by Electron Beam and Evaluation of Its Thermal Shock Resistance

High performance radiant heat shield is an important part of the metal thermal protection system for hypersonic vehicle. In order to optimize the coating process and obtain the high-performance coatings, the influences of the deposition temperature and the thickness of the coating on the residual thermal stress of the coating system were analyzed and the technological parameters of the thermal protective coating were determined. SiC/ZrO2 double layer coating was prepared on Ni-based super-alloy by electron beam physical vapor deposition, and its shock resistance was tested by one side flame heating-water cooling method. Results showed that after 80 times cycles of the thermal shock under 800℃and 900℃, macroscopic cracks were not found on the surface of SiC coating. However, after 60 times cycles under 1 000℃, cracks appeared on the surface stress concentration area of the SiC layer, and cracks expanded and became a tortoise-shell shape under the action of alternating thermal stress, and eventually led to the coating spalling. The mismatch of thermal expansion coefficient which led to the formation of the thermal stress of the coating during the thermal shock was the main cause of the coating failure.