Research On The Design Of High-temperature Resistant Coating Materials With Low Infrared Emissivity

The detection accuracy has been gradually improved with the continuous development of infrared detectors.Therefore,the high requirements for the infrared stealth design of aircraft were put forward.Especially,the speed and radiation intensity of high-speed aircraft was gradually increased owing to the concept of speed penetration,which results in a sharply increases in its surface temperature and the threat of infrared detection.To improve the survivability of battlefield,it is necessary to take effective infrared stealth measures.Compared with the normal manned aircraft,the infrared stealth of unmanned high-speed aircraft is faced with a series of problems such as complex battlefield environment,harsh service environment,high material performance requirements,multi-spectrum compatible stealth difficulty and so on,which lead to the difficult infrared stealth design for high-speed aircraft.Therefore,in order to solving the infrared stealth problem of high-speed unmanned vehicle,the infrared stealth problem and the key technical problems such as the stealth design method,high-temperature resistant coating with low emissivity,multispectral compatible stealthy performance design and high-temperature mechanical properties were systematically studied.The main contents of this dissertation include:(1)The research of the simulation calculation of surface temperature,radiation field and infrared stealth design method of high-speed aircraft.The radiation intensity of high-speed aircraft were affected by the important factors include the surface temperature and infrared emissivity.However,the surface temperature was affected by many environmental factors,which makes the design process of infrared stealth relatively complicated.Therefore,the surface temperature of aircraft under the different operating conditions was systematically studied,and the radiation characteristics and imaging calculation method was established.The radiation intensity simulation calculation of the different emissivity surface carried,the detection distance was used to evaluate the stealth performance.And then,the corresponding infrared stealth design scheme was also proposed.The research shows that the surface pressure increases and the aerodynamic heating process intensifies with the increase of the velocity of the aircraft,and the infrared radiation heat dissipation intensity weakens with the decrease of emissivity,which lead to the temperature rise continuously.The emissivity decreases from 0.8 to 0.2(3-5/8-14 μm),and the theoretical detection range reduction rate was about 47-49%when the surface temperature of the aircraft at 900 K.Therefore,the high-temperature resistant materials with low emissivity are expected to improve the infrared stealth performance of high-speed aircraft.(2)The research on the design and high-temperature resistant properties of the infrared low emissivity coating materials.The traditional coating material with low emissivity could not meet the high speed flight vehicle surface owing to the high temperature.To solve this problem,we carried on the high-temperature resistant of raw materials,coating design and performance optimization research systematically.And we were proposes a new design method for the high-temperature resistant coating material with low infrared emissivity.The mechanics performance of the coating with low infrared emissivity was improved significantly.The secondary film formation method of high temperature inorganic binder was used to solve the problem of mechanical property loss,which caused by high temperature decomposition of organic binder.As a result,the adhesion strength of the coating was higher than 4.0±0.4 MPa at high temperature of 450-600℃.The high temperature oxidation of sheet metal pigment was inhibited by the glass powder melting and heat absorption,the oxidation temperature of the coating was delayed by 35℃.To solve the coating thermal expansion mismatch problem at high temperature,the zinc powder particles with lower melting point was used.Finally,the problem of poor mechanical properties caused by thermal expansion mismatch was solved by melting the metal particles.In brief,the temperature resistance of the coating was improved from 450℃ to 600℃,the emissivity was lower than 0.35(3-5/8-14 μm),and the coating has good mechanical properties.(3)The visible-infrared-radar compatible stealth performance of high-temperature resistant coating with low infrared emissivity was studied.The influence relationship between composition and structure of low emissivity coating on visible light color,infrared emissivity and radar reflectance was studied systematically.And the visible-infrared-radar compatible stealth design method of high-temperature resistant coating material with low infrared emissivity was explored.In order to solve the problem of visible-infrared compatibility,the dark pigment with good high-temperature resistant was selected.And the design method of high-temperature resistance,low lightness and low emissivity balance of coating materials was also studied.In addition,to overcome the problem of infrared-radar compatible stealth,the design method was explored,which based on the equivalent electromagnetic parameters of the coating material.And the design and optimization of infrared-radar compatible stealth performance of the high-temperature resistant coating with low emissivity was completed,which based on the typical two-layer composite stealth coating structure.It was found that increasing the thickness of the coating,heat-treatment temperature and relative content of metal particles could reduce the low frequency radar reflectance(2-8GHz)of the composite coating,but the high frequency radar reflectance(8-18GHz)was significantly increased,the reflectance peak will gradually blue shift.(4)The optimization of binding properties and high temperature dynamic mechanical properties between the coating and carbon fiber substrate was studied.The aircraft surface has strong airflow erosion during high-speed flight.In order to meet the application requirements of the aircraft surface coating,the mechanical properties of the coating on the carbon fiber composite substrate need to be improved.Therefore,the composition and structure evolution law of low infrared emissivity coating material and the adhesion strength between the composite substrate and low emissivity coating was analyzed systematically.Then,the binding strength of the low emissivity coating material and the composite substrate was increased from 0.5±0.4 MPa to 5.0±0.4 MPa at 500℃ by using the method of coating structure design and substrate pre-treatment.In addition,to verify the high temperature erosion resistance of the coating,a high temperature and high-speed gas erosion test environment was simulated.And the high temperature dynamic mechanical properties of the coating were studied.It was found that the internal stress,caused by the decomposition of polysiloxane and the secondary film formation of glass powder,could be reduced by the high temperature pre-treatment method.As a result,the erosion resistance temperature was increased to 600±5℃,and the infrared emissivity lower than 0.35(3-5/8-14 μm).In summary,the difficulties of the surface radiation characteristics of high-speed aircraft with many influencing factors and complex mechanism were studied.And the accurate simulation calculation of the surface temperature field and radiation field of high-speed aircraft under different working conditions was realized,which based on the theoretical numerical simulation calculation method.The infrared radiation suppression effect of low emissivity materials at high temperature was obtained.In addition,the difficulty of poor high temperature infrared/mechanical properties of the coating was studied.The material design technology and preparation method were studied to achieve the integrated design of high temperature,mechanical and low infrared radiation properties of the material system.The design of visible-infrared balance of coating and the radar-infrared optimal design of composite coating were carried out,and the multi-spectrum compatible stealth design method of high-temperature resistant and low emissivity coating material was proposed.Moreover,to solve the problems of weak binding force and high-temperature erosion resistance of composite substrate under high temperature environment,the high temperature adhesion strength and erosion resistance was improved by using the structure/composition design of coating material and high temperature pre-treatment method.The development of this dissertation covers the theoretical simulation,material preparation,application research and so on.The new infrared low emissivity coating material developed has the advantages of good high-temperature resistance,low emissivity and strong erosion resistance,which expected to establish a foundation for solving the problem of infrared stealth of high-speed aircraft.