Study On Characteristics Of ZrO₂ High Temperature Coating Based On MAO Technology

Aiming at the emissivity stability of thermal barrier coating on titanium alloy surface,which can reduce the radiation temperature measurement error and improve the measurement accuracy,ZrO₂Thermal barrier coating is prepared on TC4 titanium alloy by micro arc oxidation technology.The preparation process was optimized by adjusting the working mode,current density,oxidation time,frequency,duty cycle and zirconium salt concentration.XRD,SEM,EDS,film thickness meter and roughness meter are used to analyze and characterize the surface structure and composition of the film.The emissivity measuring device is used and the thermal shock experiment is designed.The emissivity curve of the sample before and after thermal shock is measured and the average change rate of emissivity is calculated to evaluate the emissivity stability of the sample.Based on the process parameters with the minimum average change rate of emissivity,the effects of ZrO₂,Al₂O₃,Y₂O₃and Ce O₂on the emissivity stability of micro arc oxidation thermal barrier coating were studied.In order to study the effect of micro arc oxidation working mode on the emissivity of thermal barrier coating,a working mode experimental group was designed.Using(Na PO₃)₆as the main salt,K₂Zr F₆was added to provide Zr element.Five process conditions were set.Five samples were prepared in constant voltage mode and constant current mode respectively,and the samples prepared under the same process conditions and different working modes were used as the control,The experimental results show that the emissivity of the samples prepared in the constant current mode changes less before and after thermal shock,and its emissivity stability is better;Combined with the characterization of the samples prepared by the two working modes,it is inferred that the changes of film thickness and surface morphology caused by different working modes are the main factors affecting the stability of emissivity.The working mode is set as constant current.By changing the process parameters,five experimental groups found that:to prepare thermal barrier coatings with good emissivity stability,it is necessary to adjust the current density,oxidation time,frequency and duty cycle within a certain range,and ensure that the zirconium salt concentration is high enough to make the film thickness larger,the surface structure uniform and dense,the number and size of discharge micropores on the surface of the film are uniform,and the content of Zr element in the film is high,So as to ensure that the emissivity of thermal barrier coating changes less before and after thermal shock.In the experimental range,the experimental group with the best emissivity stability is the current density of 4 A/dm~2,oxidation time of 40 min,frequency of 500 Hz,duty cycle of 20%,zirconium salt concentration of 20 g/L.the average change rates of emissivity at five temperature points in 650?850?are 0.018,0.017,0.023,0.025 and 0.024.By adding oxide particles to the electrolyte,it is found that the addition of Al₂O₃can improve the emissivity stability of the coating,but excessive will reduce the emissivity stability of the coating;The addition of Ce O₂will reduce the emissivity stability of the coating;The addition of ZrO₂and Y₂O₃can improve the emissivity stability of the coating,and the latter has the best improvement effect on the emissivity stability.When 6 g/L is added,the average emissivity change rate of five temperature points can be reduced to 0.009,0.009,0.009,0.008 and 0.008.The optimization effect is the most obvious at 800?,and the average emissivity change rate is reduced by 0.017.