| Thermal barrier coatings (TBCs) have been widely used for protecting the superalloys from high temperature, oxidation and corrosion. The increasing demands for high performance superalloys in the turbine engines make TBCs a key component in combating degradation resulting from failure mechanisms. Therefore, high quality TBCs and advance fabrication process have been one of the important corners of materials science. In this study, multiple-layer TBC system was simultaneously synthesized on Ni superalloy substrate by spark plasma sintering (SPS) process, and the best parameters in SPS for high performance TBC were established.Nano-structured 7YSZ/Al2O3/Ni-343 multiple-layer TBCs with various microstructure were produced by SPS from nano ZrO2-7wt.%Y2O3 (7YSZ) powder, Al foil and nano Ni-343 powder made by cryomilling method. Afterwards, the mechanical properties arid high temperature behavior of 7YSZ/Al2O3/Ni-343 TBC and Ni-343 bulk sample were studied by advance testing techniques.The results indicated that, the grain size of Ni-343 powder was efficiently reduced to 20-70 nm by cryomilling method, and the microstructure and performance of TBCs were improved by SPS process. The best fabricating parameters were established as:a 500μm thick 7YSZ top coat, a 150μm thick Ni-343 bond coat, sintering at 1000℃, pressing under 50MPa axial pressure and dwelling for 3min at sintering temperature. Compared with conventional TBC, the performance of nano-structured TBC, such as bonding strength, oxidation-resistant behavior and thermal cycling life, was significantly improved by excellent microstructure between 7YSZ top coat and Ni superalloy substrate. The thermally growth oxide (TGO) in nano-structured TBC grew slowly and homogeneously, which enhanced high temperature performance of the TBC system.The research on Ni-343 alloy indicated Nano-structured fully dense Ni-343 bulk sample was strengthened by the mechanism of fine grain strengthen. The microhardness of Ni-343 bulk sample was influenced by microstructure and phase composition which determined by heat treatment conditions. In this dissertation, a novel technique for preparation of TBCs has been introduced, which characterized as simultaneous synthesis of a multiple-layer structure in simple process. The results from this research should be great helpful to the development of TBCs. |
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