Thermal barrier coating system towards high strain tolerance and sintering resistance: design, manufacturing, and characterization

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As a novel coating deposition method for thermal barrier coating (TBC), suspension plasma spraying (SPS) takes advantages of conventional air-plasma spraying and vapor deposition technologies, by combining porous with columnar microstructure. Moreover, using suspension feedstock facilitates the employment of nano-sized powder, which leads to an ultra-fine microstructure. Combing these microstructure features, graded or multilayered SPS TBC is a potential candidate for multi-functional applications. However, few systematic studies on multi-functional SPS TBC have been reported in literature.According to our previous investigations, various microstructures, e.g. columnar and vertically cracked structures, can be fabricated by adjusting spraying parameters. In the columnar microstructure, relatively high porosity and crack density is beneficial to prolong thermal cycling life, owing to the high strain tolerance. By reducing the vertical crack density, sufficient corrosion resistance by avoiding the penetration of molten oxides deposited from inlet gas can be achieved. With tailored porosity, diffusion controlled sintering process may be suppressed. In principle, deposited by adjusting spraying parameters, structurally graded SPS TBC will provide multiple functions at low cost.In this project, the design method and manufacturing roadmap for structurally graded SPS TBC using yttria stabilized zirconia (YSZ) will be established, based on relationships between spraying parameter, microstructure and mechanical property. Microstructural and mechanical evolutions will be characterized by thermal shock, hot corrosion and sintering processes, using high-resolution microscopy / tomography and in-situ measurements. Degradation and failure mechanisms will be elucidated through finite element method, with a coupling constitutive model and multi-cracking algorithm employed. Based on experimental and numerical results, evaluation criteria and optimized microstructure design will be proposed for multi-functional performances in quasi-service condition. The completion of the project will provide further insights on the structure-dependent degradation mechanisms and lay foundation to the integration of various microstructures for multiple functions. Furthermore, the concept of microstructure design will inspire the application of advanced TBCs using new compositions beyond YSZ.