Study On The Anti CMAS Corrosion Behavior Of YSZ Thermal Barrier Coating Modified By Laser Remelting

The Y₂O₃partially stabilized ZrO₂(abbreviated as YSZ)thermal barrier coating prepared by plasma spraying is widely used to increase the operating temperature of hot end components such as high-pressure turbine blades of aircraft engines because of its lower cost and higher thermal insulation.However,during its service,low-melting calcium magnesium aluminum silicon particles(Ca O-Mg O-Al₂O₃-SiO₂,CMAS)brought into the atmosphere and dust will be deposited on the surface of the thermal barrier coating,causing the thermal barrier coating to fall off and fail.Seriously jeopardize the safe operation of the engine.In this paper,laser remelting technology is used to modify the surface of the YSZ thermal barrier coating prepared by plasma spraying,in order to improve the thermal barrier coating's resistance to CMAS high temperature corrosion.Study the structure evolution of laser remelting YSZ thermal barrier coating,explore the effect mechanism of laser process parameters on the coating structure,and study the anti-CMAS corrosion mechanism of laser remelting layer.The specific research is as follows:(1)The microstructure evolution of YSZ thermal barrier coatings with different laser specific energy remelting was studied.The experimental data showed that after the laser remelting process was used to modify the coating,the defects such as pores and cracks in the sprayed coating structure were Eliminate,the layered structure in the form of mechanical bonding is transformed into a dense remelted layer structure combined with chemical metallurgy.In the process of laser remelting,the size of laser specific energy affects the degree of remelting and the improvement of tissue pores.When the laser specific energy is 22.22J/mm²,the degree of remelting is the smallest,the depth of the remelting layer is 180?m;the laser specific energy is 66.67J/mm²,the improvement of the pore structure of the coating is the best,and the porosity is reduced from 21.4%to 1.9%.(2)Explore the influence mechanism of laser power,scanning speed and laser lap rate on the structure of the remelted layer.The results show that:the laser power has the greatest influence on the density of the remelted structure,when the laser power is 700W,the density of the melt layer structure can reach 93.9%;the laser overlap rate has a great influence on the quality of the remelting molding,when the overlap rate is 25%,it can effectively reduce the phenomenon that the laser remelting energy is continuously injected into the molten pool and causes the stirring stripe area;scanning speed has little effect on the remelting of the coating,when the scanning speed is 120mm/min,the slower scanning speed helps the uniform formation of the remelted layer.Comprehensive analysis,the better laser remelting process parameters are:laser power 500W;scanning speed 120mm/min;spot diameter 3mm;laser overlap rate 25%.(3)The mechanism of the laser remelted layer's resistance to high-temperature corrosion of CMAS was studied in detail.The experimental results show that after the molten salt CMAS corrodes the YSZ coating,the phase structure of the surface layer changes,and spherical m-ZrO₂particles with a size of 0.5?m-1?m appear inside the coating.The formation of MgAl₂O₄increases the internal stress and causes crack initiation and expansion;After laser remelting,the microstructure of YSZ coating is dense,it hinder the diffusion of Ca,Mg,Al and Si elements of CMAS molten salt.The phase transformation degree of ZrO₂structure was reduced,the formation of corrosion products was reduced,and greatly improves the coating's resistance to CMAS high-temperature corrosion.