Preparation Of Low Emissivity Multilayer Films And Investigation Of Infrared Radiation Characteristics

Zirconium diboride（ZrB₂）is one of the most studied materials in the ultra high temperature ceramics（UHTC）category.Because of its high melting point and high hardness,good mechanical properties,electrical properties and thermal shock resistance,it is widely used as thermal protection.System materials,electrode materials,and nuclear control materials.In addition,these unique properties make ZrB₂-based ceramics particularly suitable for aerospace and aerospace applications,including rocket nozzles,nozzle exit ramps,and aircraft leading edges.This article takes ZrB₂-based ultra-high temperature ceramic materials as the background for high-temperature infrared stealth applications.As a high-temperature infrared low-emissivity material,the main problem currently facing ZrB₂ is its high-temperature oxidation.Based on this,a series of exploratory studies have been performed.In this paper,ZrB₂ single-layer films and samples of ZrB₂/Al₂O_3,ZrB₂/CeO₂ double-layer low-emissivity films were prepared by magnetron sputtering,and the improvement of the anti-oxidation properties of ZrB₂ single-layer films was investigated.as follows:A single-layer ZrB₂ film was prepared by DC magnetron sputtering,and the related mechanism of heat treatment affecting the infrared performance of ZrB₂ film and the high-temperature oxidation behavior of the film were explored:ZrB₂ film has excellent infrared stealth performance,and the average reflectance of 2¹4um is only 0.94;The film has a certain temperature resistance at 600°C.The film performance is stable and there is no significant change in infrared emissivity during heat treatment for 2 hours.However,as the heat treatment time increases to 10 hours,the high temperature oxidation of the film reduces the average infrared reflectance of the film from 2 to 14um from 0.94to 0.75,and as the heat treatment time continues to increase,the performance of infrared stealth continues to deteriorate,unable to meet the application requirements of infrared stealth;the temperature of the film exceeds 700℃,the oxidation of the film intensifies,and the film has failed after a short period of heat treatment.In order to improve the high-temperature oxidation resistance of zirconium boride films,ZrB₂/CeO₂ double-layer films of different thicknesses were prepared on the ZrB₂film by RF magnetron sputtering.The visible-infrared characteristics and high-temperature oxidation resistance of the films were investigated.The wide forbidden band width makes CeO₂ films have very high transmittance to visible and infrared light;ZrB₂/CeO₂ films of different thicknesses have certain interference effects on light in different wavelength bands,and the CeO₂ layer plays a role of antireflection film;at high temperatures Diffusion of the O element in CeO₂ results in no significant increase in the oxidation temperature of the double-layer film compared with the ZrB₂ single-layer film.In view of the adverse effects of the diffusion of O element in CeO₂ on the composite film,ZrB₂/Al₂O₃ double-layer films of different thicknesses were prepared on the ZrB₂film by RF magnetron sputtering in place of the oxide insulation layer.The oxidation resistance was investigated:the double-layer film still had an average reflectance of 0.90after heat treatment at 600°C for 30h,and the infrared performance slightly decreased after heat treatment at 750°C for 2h.The reflectance of the film was 0.86.After the temperature increased to 800°C,many fine cracks were generated on the surface of the film after heat treatment,and the reflectance of the film decreased to 0.76.The addition of the Al₂O₃ layer effectively isolates the oxygen element in the air,and does not affect the infrared characteristics of ZrB₂,while increasing the oxidation temperature of the single-layer film.