In-situ Preparation Of Antistatic Thermal Control Coatings On Aluminum Alloy And Their Space Environmental Adaptability

Thermal control coating can realize the thermal control by adjusting the optical and thermal properties of material surface,which is an important material to ensure the normal operating temperature of spacecraft in orbit.The antistatic inorganic thermal control coating with low absorption/radiation ratio has excellent stability in space environment and plays an important role in ensuring the temperature level of spacecraft in space environment,equipotential design of the whole spacecraft and thermal design of optical system.With the fast development of aerospace technology,higher demands are put forward for the performance of thermal control coating.Based on the engineering application background,this paper adopts liquid phase plasma electrolytic oxidation（PEO）and atomic layer deposition（ALD）technology to construct a low absorption/radiation ratio antistatic thermal control coating with excellent space environment adaptability on the aluminum alloy surface,which provides theoretical and technical support for the thermal control materials selection of spacecraft.Al₂O₃-Zn O-Y₂O₃ thermal control coating with low solar absorption ratio and high emissivity was in-situ grown on aluminum alloy surface by PEO technology.SEM,XRD,XPS and other analytical instruments were used to study the effect of electrolyte composition,types and amount of rare earth elements,and power supply parameters on microstructure,phase composition and thermal control performance of Al₂O₃-Zn O-Y₂O₃ thermal control coating.The results show that the performance of Al₂O₃-Zn O-Y₂O₃thermal control coating is optimum at the electrolyte composition of 30 g/L Na₂H₂P₂O₇,20 g/L Na₂Si O₃,10 g/L Zn（H₂PO₄）₂,10 g/L Na₂EDTA,8 g/L KOH and 6 g/L Y（NO₃）₃?6H₂O,current density of 10 A/dm²,the power frequency of500 Hz,the power duty ratio of 30%and the oxidation time of 15 min,respectively,and its emissivity,solar absorption ratio and radiation/absorption ratio are 0.859,0.405 and 0.471,respectively.Al₂O₃-Zn O-Y₂O₃thermal control coating has a typical crater-like morphology,which is mainly composed of main phase Al₂O₃,Zn O and Y₂O₃.In order to give the antistatic ability of Al₂O₃-Zn O-Y₂O₃ thermal control coating,aluminium-doped zinc oxide（AZO）conductive film was deposited on the surface of Al₂O₃-Zn O-Y₂O₃ thermal control coating by ALD technology,and the AZO/Al₂O₃-Zn O-Y₂O₃ antistatic thermal control coating was obtained.The effects of deposition parameters on coating composition,structure,electrical conductivity and thermal control performance were investigated.The results show that the obtained AZO/Al₂O₃-Zn O-Y₂O₃ composite coating has the best comprehensive performances when the deposition temperature,pressure,Zn-Al ratio and cycle period are 150℃,0.15 Torr,24:1 and 6 cycles,respectively.The resistivity,emissivity,solar absorption ratio and absorption/radiation ratio are 1.15×10^-3Ω?cm,0.892,0.409 and 0.459,respectively.Compared with Al₂O₃-Zn O-Y₂O₃ thermal control coating,the introduction of AZO not only gives the antistatic ability of Al₂O₃-Zn O-Y₂O₃ coating,but also improves the thermal control performance of the coating.The microstructure analysis and finite difference time domain show that the surface and pores of Al₂O₃-Zn O-Y₂O₃ coating prepared by PEO technology are covered by AZO nano-island structure,forming the uniform micro-nano structure,which can effectively improve the emissivity of the coating in the wavelength range of 2-30μm.Space environment test is an essential step for the formal application of new materials on spacecraft.In order to verify whether the coating meets the requirements of spacecraft,the changes of the structure,composition and properties of the coating after vacuum-electron irradiation,vacuum-ultraviolet irradiation,atomic oxygen and vacuum thermal cycling tests were comprehensively investigated according to GJB2502.2-2006 test requirements.The results show that with the increase of electron irradiation fluence and the extension of UV irradiation time,the resistivity of the thermal control coating improves to about three times,compared with initial resistivity,the solar absorption ratio firstly increases and then basically remains unchanged,and the emissivity is basically unchanged.When the electron irradiation fluence reaches 2.0×10¹⁶ e/cm²,the solar absorptance increment of the modified coating decreases from 0.038 to 0.015.When the irradiation time reaches 2000 ESH,the absorptance increment of the modified coating decreases from 0.030 to 0.028,and the established UV irradiation life prediction model shows that when the irradiation time is extended to 25000 ESH,the degradation degree of absorption of Al₂O₃-Zn O-Y₂O₃ thermal control coating（Δα_S=0.0902）is about twice than that of AZO/Al₂O₃-Zn O-Y₂O₃composite coating（Δα_S=0.0536）.The above results show that the modification of AZO conductive film can effectively improve the resistance of the coating to space electron irradiation and UV irradiation.In addition,the results of atomic oxygen,thermal cycling and damp heat test show that the state and properties of coating could not be obviously varied,which can meet the application requirements.On this basis,the traction is based on the application demand of antistatic thermal control coating on the surface of XX model exposed aluminum alloy electric control box.According to the size and structural characteristics of the electric control box,based on the finite element analysis results of the electric field line distribution,the auxiliary electrode was designed to regulate the edge effect,and the liquid plasma electrolytic oxidation technology was obtained to meet the requirements of the surface implementation of the electric control box,which effectively solved the problem of edge effect caused by the edge ablation.The antistatic thermal control coating with low absorption/radiation ratio and good combination with substrate was prepared on the surface of electric control box by atomic layer deposition technology.The area density of the obtained coating was as low as～92 g/m² and the bonding strength was as high as～5.5MPa.Solar absorption ratio,emissivity and conductivity can meet the demand,providing material basis and technical support for the development of XX model aluminum alloy electric control box,which can effectively improve the spacecraft lightweight level and in-orbit reliability.