等离子喷涂YSZ热障涂层的工艺研究

Plasma Spraying Process of YSZ Thermal Barrier Coatings

目的优化大气等离子喷涂工艺,提高热障涂层的耐腐蚀性能与热循环寿命。方法设计正交试验,制备出不同工艺参数的YSZ涂层。用共聚焦显微镜、X射线衍射仪、能谱分析仪对涂层的表面粗糙度、表面与截面形貌、元素组成与分布进行表征,用ImageJ软件分析涂层的孔隙。根据试验数据优化工艺参数,对比分析工艺优化前后涂层的耐腐蚀性与热循环寿命。对涂层进行热震水淬试验,分析涂层的热震寿命与失效行为。结果不同工艺下制备的涂层在孔隙、耐熔盐腐蚀与热循环寿命方面存在明显差异,工艺参数W3X3Y1Z3组合为优化出的喷涂工艺。采用优化后工艺所制备的涂层TBC-1,孔隙率为9.65%,平均孔隙尺寸为6.18μm^(2),未观察到明显的大孔与裂纹。涂层表面粗糙度为3.48μm,粉末熔化状态较好。热腐蚀之后,涂层截面熔盐元素V的质量分数为2.03%,无熔盐积聚现象。涂层经20次热腐蚀与热冲击联合试验后,质量损失率为0.25%,表面完整,无明显剥落。TBC-1在热震试验中的失效形式为涂层大面积剥落,失效次数为172次。结论等离子喷涂的工艺参数对涂层的综合性能有重要影响,涂层中较大的裂纹和孔隙可作为熔盐的渗透途径,加速涂层的腐蚀,同时使热循环寿命变差。经优化后工艺制备的涂层,内部孔隙分布均匀,且平均孔隙尺寸较小,表现出良好的耐腐蚀性与热循环寿命。涂层中热生长氧化物(TGO)的生长应力、陶瓷层与黏结层的热失配应力是涂层中裂纹扩展和涂层失效的重要原因。

To enhance the corrosion resistance and thermal cycling life of thermal barrier coatings(TBCs),the optimization of atmospheric plasma spray(APS)processes has emerged as a pivotal research direction.Given the complexity of factors affecting coating quality,this study examined four primary spray parameters:current,main gas flow rate,powder feed rate,and spray distance.Each parameter was set at three distinct levels.Using an orthogonal experimental design,nine YSZ coatings with differing processes were fabricated.A mixed salt of Na2SO4 and V2O5(with a 1∶1 mass ratio)was applied to the coating surface at 15 g/cm^(2),after which the samples were placed in a muffle furnace set at 900℃for 6 hours of corrosion.To simulate the real-world operational environment of TBCs,the post-corrosion samples were cooled to room temperature and then placed in a heat-treatment furnace at 1150℃.The samples were quenched in water every 10 minutes.The surface changes in the coating after 20 cycles were observed.The surface roughness,morphology(both surface and cross section),and elemental composition and distribution of the coating were characterized by confocal microscopy,X-ray diffraction(XRD),and energy dispersive spectroscopy(EDS).ImageJ software was employed to analyze the pore size and distribution of the coating.The combined metrics of the coating's porosity and the mass loss rate post combined thermal corrosion and shock tests were utilized as evaluative parameters for the coating's overall performance.The range analysis method was adopted to transform multiple parameter indicators into a single criterion for process optimization.A comparative analysis was conducted between the coating from the optimized process and the nine coatings from the orthogonal tests.The optimized coatings were placed in a muffle furnace set at 1150℃,with each 5-minute hold followed by quenching in water,counting as one cycle.The number of thermal shock failures was recorded,and the failure behavior of the coating was analyzed.Results revealed evident disparities in porosity,molten salt corrosion,and thermal cycle life for coatings prepared under different processes.The range analysis method identified the W3X3Y1Z3 parameter combination as the optimized spray process.For the TBC-1 coating prepared through the orthogonal experiment-optimized process,the porosity stood at 9.65%,with an average pore size of 6.18μm^(2).No obvious large pores or cracks were observed.The coating's surface roughness was 3.48μm,and the powder exhibited a satisfactory melting condition.For post thermal corrosion,the cross-sectional content of the molten salt element V in the coating was 2.03%,with no signs of salt accumulation.After 20 combined thermal corrosion and shock tests,the coating's mass loss rate was only 0.25%,maintaining an intact surface without noticeable spalling.The failure mode of the optimized coating in thermal shock tests was extensive coating delamination,with a failure occurrence at 172 cycles.In conclusion,APS process parameters significantly influence the comprehensive performance of coatings.Larger cracks and pores in the coating can serve as pathways for molten salt permeation,accelerating coating corrosion and diminishing thermal cycling life.Coatings prepared after process optimization,with uniform internal pore distribution and smaller average pore sizes,exhibit superior corrosion resistance and thermal cycling life.The growth stress of the thermally grown oxide(TGO)and the thermal mismatch stress between the ceramic and bond coat layers are crucial factors contributing to crack propagation and coating failure.