| High energy pulse cathodic micro-arc electro-deposition method is used in two kinds of solution systems to prepare ZrO2and ZrO2-Y2O3composite ceramic thermal barrier coatings on the surface of aluminum alloy, and the effect of different electrical parameters, different solutions on the thickness and heat insulation temperature of the coating is analyzed by the orthogonal test method and the optimal process is obtained. Moreover, the properties of the coatings is measured by some methods. Based on the growth process and microstructure morphology, the cathodic micro-arc deposition discharge mechanism and the physical model is established; finally, the thermal stress coupled field is calculated by the finite element numerical simulation software ANSYS.The experimental data show when the thickness of fabricated barrier coating is3μm and the plate-distance is10mm during the process of the reaction, and the optimal process is analyzed by range method to get the optimal plan, which is:solution concentration of0.03mol/L, duty ratio of20%, frequency of600Hz and current density of10A/dm2. According to the optimization process, ZrO2coating has been prepared with the thickness of19.5μm, thermal insulation temperature of47.05℃, the arc voltage of160V, the hardness of791.5HV, surface roughness of3.241μm and the adhesion strength of32N. With the addition of Y(NO3)3, composite coating thickness has been prepared with the thickness of26.8μm, thermal insulation temperature of59.1℃, the arc voltage of152V, hardness of880HV, surface roughness of3.727μm and the adhesion strength of58N.In Zr(NO3)4solution system, the equation of coating thickness-time is y=-8.74+1.43x-0.0156x2. When Y3-is added, the thickness of the coating increases along with the content of Y3+first increases and then decreases. When the Y3+content is8wt%, the thickness reach its maxium, and the equation of coating thickness-time is yl=2.108x+17.90within15min and then y2=0.0455x-2.015x+66.9. SEM observation reveals that the coating is of flat surface pores cross-section and bite-like combination with the matrix. The main components of ZrO2coating in Zr(NO3)1solution system is ZrO2and coating in Y(NO3)3-Zr(NO3)4solution system is ZrO2and YSZ while the main phase is m-ZrO2,t-Zr0.92Y0.08O1.96-0.04,Al2O3,Y2Si2O7and Si. The calibration results of coating in Zr(NO3)4solution system by TEM shows that the zone axis is [444].The coating growth-process can be divided into three stages which include pre-sparks stage, micro-arc stage and partial arc stage. The physical model of coating growth mechanism consists four steps as electrolysis, deposition, discharge and sintering. The sintering temperature and Y2O3content have influence on the coating stability of ZrO2. The coating has the maximum solid stability of the cubic phase when the Y2O3content is8wt%and the sintered temperature is1200℃. The results of numerical simulation show that the coating thickness has an approximately proportional relationship with the insulation temperature, and the coating thickness of50μm has the insulation temperature of15℃. The calculation results of thermal residual stress field show that the coating thickness of50μm has the highest thermal stress and200um has the minimum. |
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