Finite Element Study Of Temperature Field And Stress Field Of Laser Cladding YSZ@Ni Coating

During the ues of YSZ thermal barrier coating,laser cladding of nano YSZ@Ni core-shell particles is an effective way to solve the problems of crack generation and poor bonding with substrate.However,laser cladding is a rapid heating and condensation technology,which temperature change has significantly influence on the microstructure and properties of the coating.In the rapid condensation process,a larger residual stress will lead to cracks in the cladding.Moreover,it is difficult to detect the temperature and stress fields in the process of laser cladding.In this paper,the temperature and stress field of YSZ thermal barrier coating prepared by laser cladding were simulated by ANSYS software,and the melting behavior of the cladding layer and the crack formation mechanism of the thermal barrier coating were investigated.Firstly,the temperature field of laser clad YSZ@Ni nanoparticles was simulated and analyzed.The error of the 3D model in depth direction and width direction is 4.51%and 8.23%,respectively,in which the accuracy is higher in depth direction.In the process of laser scanning,the temperature field is similar to the scoop shape,front end isotherm of molten pool was concentrated and with a significant temperature gradient,back end isotherm of molten pool was sparsed and with small temperature gradient.By comparing the temperature distribution curves of different directions and distances,founding that the maximum temperature of the measured point appears hysteresis,and the farther away from the spot center,the more obvious the hysteresis.The simulation results of orthogonal experiment show that the variation law of significant influence of process parameters(scanning speed,V,laser power,P,spot diameter,d)on the size(width and depth)of molten pool was P>V>d,the change law of significant influence of technological parameters on the peak temperature was P>d>V and the variation law of significant effect of technological parameters on energy utilization rate was V>d>P.Secondly,based on the simulation of the temperature field of three different powders of laser preset cladding(YSZ@Ni,YSZ/Ni,YSZ),the melting behavior of the cladding layer is revealed.Through the simulation calculation of the temperature gradient,solidification cooling rate and solid-liquid interface rate of the front end of molten pool,which found from the bottom to the top of the molten pool,there were planar crystal,cellular crystal,coarse and fine equiaxed crystal surface,respectively.The cooling rate in solidification was YSZ@Ni>YSZ/Ni>YSZ,and the size of the molten pool was YSZ@Ni<YSZ/Ni<YSZ.The results shows that the peak temperature of lasercladding YSZ and YSZ/Ni powder burning phenomenon occurred,the discontinuous YSZ coating,coating thickness,uneven and adhesive layer of matrix,cracks,porosity and other defects,and microstructure of the coatings YSZ@Ni core-shell particles were prepared by homogeneous,good continuity.Compared with the results of laser cladding YSZ and YSZ/Ni powder,YSZ@Ni minimum pool size,the lowest dilution rate,and the results show that the element diffusion bonding layer at the elements closer to the substrate,the YSZ@Ni coating and substrate with good metallurgical,not easy to fall off.Finally,the crack formation mechanism of the coating was investigated based on the thermal stress coupling simulation.It was found that the cladding layer presents a tensile stress state,the stress at both ends was more larger and the specimen was warped upward,and these phenomena was all due to the cooling shrinkage of the molten pool material after laser cladding.The tensile stress between the substrate and the YSZ coating is biggest in the X direction,which is easy to produce transverse cracks perpendicular to the scanning direction.Comparison of laser cladding different powder(YSZ,YSZ/Ni,YSZ@Ni)stress field simulation results showed that the maximum stress sequence of the bonding layer during the laser cladding process was:YSZ>YSZ/Ni>YSZ@Ni,and the order of plastic strain magnitude at the bonding layer in the heat stable region was :YSZ>YSZ/Ni>YSZ@Ni.So The possibility of crack generation in laser cladding YSZ powder is the biggest,YSZ@Ni core-shell particles have the least chance of cracking.