Study On Thermal Barrier Coatings Of Gas Turbine Blade

With the development of industry, the gas inlet temperature and efficiency of gas turbine have been improved continuously. However, the existing superalloys and cooling technology cannot meet this need. Thermal barrier coatings(TBCs) is the most advanced high temperature protective coatings with good high temperature performance which can produce large temperature drop between high temperature gas and metal parts, prolong the service life of the engine parts and improve the thermal efficiency of engine parts.In this work, TBCs which consisted of a NiCo Cr Al Y bond coat( BC) and a Zr O2-8w.%Y2O3 top coat( TC) was prepared on the nickel-base superalloy. It was well-established the microstructure and properties of TBCs could vary enormously depending on their manufacturing method. BC was prepared by high velocity oxygen fuel(HVOF) spraying technology, which could significantly improve interface rough.The grain was refined, which increased the spread channel of Al element in coat and helped to form Al2O3 layer. Bond coat was sprayed by different spray distance、oxy-fuel flow and cooling air, and the influence of spraying parameters on the coating was studied.In these coatings prepared under different parameters, the paper selects the best coating to in-depth study. TC was prepared by atmospheric plasma spraying( APS). The relationship between bonding strength and spraying distance, powder feed rate, spraying current and primary gas flow rate were analyzed and the optimum parameters were acquired. The microstructures of TBCs were investigated thoroughly by scanning electron microscopy( SEM). The porosity, bonding strength, thermal conductivity,thermal insulation property and thermal shock resistance were test.The double-layer thermal barrier coatings were prepared on the metal substrate which thermal expansion coefficient of ceramic coat cannot match the thermal expansion coefficient of metal substrate. During the working process, the violent change of temperature will cause the coating to produce the thermal stress, which can lead to the failure of the coating. In order to reduce the thermal stress of coatings, the concept of functional gradient materials(FGM) is introduced to the thermal barrier coating.According to the concept, gradient thermal barrier coatings was designed which composition and performance is continuously changed from the matrix to the ceramic surface. And gradient thermal barrier coatings can greatly reduce thermal stress due to the mismatch of generated thermal expansion coefficient and avoid the spalling of coatings during the thermal shock process. Based on the four factors and three levels,orthogonal test was used to study plasma spraying technology by spraying distance,powder feed rate, spraying current and primary gas flow rate. And the influences on the porosity of gradient transition layer were studied too. Finally, the bonding strength and the thermal shock resistance were test. The experimental results show that the bonding strength and thermal shock life of the gradient TBCs has been enhanced compared with double-layer TBCs. Transition layer can eliminating the mutation of the coating composition, reduce the thermal stress concentration of coating in the thermal shock process and delay the formation of thermal shock crack, so the thermal shock resistance of graded thermal barrier coatings is better.