Study On The Fabrication And Performance Of VO₂/HfO₂/Al Smart Thermal Control Coating

The implementation of complex missions such as deep space exploration has made spacecraft face more complex and harsh space thermal environments,posing a huge challenge to existing thermal control materials.Smart thermal control coatings based on VO₂ have the advantages of passive control,narrow phase transition range,and strong designability.However,its practical application is limited by the problems of small infrared（IR）emittance tunability and high phase transition temperature.Based on the opti cal properties of VO₂,the Fabry Perot resonant cavity（F-P）structure has been designed.Besides,the research on the preparation process and dynamic regulation characteristics of VO₂/HfO₂/Al smart adaptive thermal control coatings has been conducted.And the environmental aging behavior and environmental stability evaluation ha ve been further studied,providing theoretical support for the research of smart thermal control coatings in China.The main research is as follows:The VO₂/HfO₂/Al smart thermal control coating was designed based on the F-P cavity structure.The influence of VO₂ layer thickness on the IR spectrum of F-P structure was studied.Besides,by using skin depth calculations,normalized electric field and resistance loss simulations,the physical mechanism of the influence of VO₂ thickness on the thermal radiation regulation of F-P structure was revealed.At the same time,the critical thickness for the transformation of IR radiation characteristics of the F-P structure was discovered.Through IR spectrum simulation and IR emittance calculation,the influence of VO₂ layer,HfO₂ layer and Al layer thickness on the change of IR emittance tunability of F-P cavity structure was obtained.Furthermore,the optimal film thicknes s range of VO₂/HfO₂/Al smart thermal control coating design was obtained based on the working principle of interference cancellation in asymmetric F-P cavities.The simulation-optimization results show that when the thickness of the VO ₂ layer was 60 nm,the thickness range of the HfO₂ layer was 500-1200 nm,and the thickness of the Al layer was thicker than 60 nm,the emittance tunability at 2.5-25μm can reach more than 0.50.VO₂/HfO₂/Al smart thermal control coating was prepared by high-power impulse magnetron sputtering（Hi PIMS）and direct current magnetron sputtering technology（DCMS）.Firstly,the influence of preparation processes for each functional layer on its performance was studied to determine the optimal preparation parameters for each functional layer.Secondly,thermal control coatings were prepared,and it was verified that adjusting the thickness of VO₂ layer and HfO₂ layer was an effective method to adjust the maximum absorption peak position and IR emittance of the coating.Based on the asymmetric F-P resonance effect and the phase transition characteristics of VO ₂,the structure achieves IR thermal radiation changes of low emission at low temperatures and high emission at high temperatures.Based on the asymmetric F-P resonance effect and VO₂ thermally induced phase change characteristics,the IR thermal radiation changes of low emission at low temperature and high emission at high temperature are realized,and excellent infrared emittance tunability（Δε2.5～25μm=0.51）in the range of 0～60℃is obtained.In addition,2at%W doping reduces the phase transition temperature（T_c）of VO₂,then the T_cof VO₂/HfO₂/Al thermal control coating is lowered to 27.5℃,close to RT.Through demonstration and verification experiments,as well as single board level vacuum heat balance tests,the dynamic adjustability of the thermal control coating has been further demonstrated.The variation in radiation power density can reach 196.3 W/m² within the range of 0～60℃,exhibiting excellent low-temperature insulation and high-temperature heat dissipation effects.According to the actual application requirements,the environmental stability of VO₂/HfO₂/Al smart thermal control coatings was studied.According to the actual storage environment,aging tests were conducted in natural and humid environments.By characterization analysis,it was shown that the coating has high density,adhesion,and crystallinity.Although the surface layer had an aging phenomenon,the degradation depth of VO₂ film was less than 20 nm.After aging 80 days at natural environment,the thermal control coating still exhibited excellent phase transition properties.In addition,after being stored in a high temperature and humidity environment of 50℃and 90%RH for 102days,the phase change properties of the coatings remained basically unchanged,which could be equivalent to being stored for 7.7 years in an environment of 25℃and 60%RH.The thermal shock test was conducted at-196～150℃according to the environmental change of high and low temperature alternation in space.After 700 thermal shocking cycles,the coatings still have good adhesion,the surface is good,and no film falling off or cracks occur.The IR emittance tunability is basically without attenuation,maintaining excellent environmental stability.