Preparation And Properties Of Steam Turbine Blade Thermal Barrier Coating Based On Laser Cladding

As an important part of the modern power plant, boiler steam turbine has a great influence on the efficiency of the power generation. Development of ultra-super critical thermal power units above 700℃ can effectively improve the utilization of coal, reduce energy consumption and CO2 emissions is the direction of thermal power plant’s development. Blade is one of the most important parts of steam turbine, in the turbine bear transformed the steam heat energy into mechanical energy of the important tasks. Its working environment is extremely bad generally and occurs high temperature oxidation corrosion, abrasion and high temperature creep destruction. The development of high temperature blade material is one of the key problems in the construction and operation of the advanced ultra-super critical unit. Thermal barrier coatings (TBCs) is the resistance of high temperature and low thermal conductivity of ceramic materials in coatings and metal composite phase, thereby reducing under the environment of high temperature metal surface temperature of a thermal protection technique can significantly reduce the surface temperature of the turbine blade alloy, prolong the working life of the blade is greatly and improve the thrust and efficiency of the engine.Thermal barrier coatings are prepared on the surface of turbine blade materials (304 stainless steel and 1Crl3 stainless steel) with laser cladding and plasma spraying processes. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) are used to analysis the microstructure, composition distribution and phases of thermal barrier coatings. high temperature oxidation and thermal shock resistance are used to test the thermal barrier coatings anti high temperature oxidation resistance and thermal shock resistance. The results are as follows:(1)CoCrAlY alloy powders were prepared for the bond coat by different laser power and scanning speed (P=2.5kW/3kW; v=4,8,12mm/s). The microstructure of the cladding layer is uniform, compact, without crack and porosity, and it forms a good metallurgical bond with the substrate, the hardness of the cladding layer is significantly improved than that of the substrate. Through the analysis of the results, it is concluded that the laser power 2.5kW, scanning speed 8mm/s cladding layer quality is the best. By using vertical and the same direction of laser scanning method to prepare a double lap cladding layer, when the lap ratio is 16.7%, the surface of the cladding layer is the most smooth.(2) 8wt%Y2O3-ZrO2(8YSZ) ceramic coat was prepared on the surface of the bond coat by plasma spraying, and the thickness of the coating was about 200μm. The high temperature oxidation resistance and thermal shock resistance of the coating samples were tested. The results show that the weight of the sample increased by approximately 4.1mg·cm2 after 750℃ and 108h constant temperature oxidation in resistance furnace, the ceramic coat is mostly off the surface of the sample after 40 thermal shock test.(3)After 750℃ temperature oxidation, the residual stress of the ceramic coat is about 496.5Mpa pressure stress, the residual stress of the bond coat is 23Mpa tensile stress, the residual stress of the substrate is about 6Mpa tensile stress. By laser micro Raman spectroscopy measurements, the residual stress of ceramic surface coat is 434.78Mpa pressure stress.