Preparation And Infrared Characterization Of ZrB₂ Films Based On Alloy Substrates

As the flight speed of hypersonic aircrafts increases,the aerodynamic heating during the flight process will lead to a skin temperature of over 400°C.Traditional infrared stealth materials will be rapidly oxidized at this temperature,leading to a rapid deterioration of infrared radiation properties.Therefore,zirconium boride（ZrB₂）,an ultra-high temperature conductive ceramic（UHTC）with high melting point,high electrical conductivity,high hardness and stable chemical properties,has gained the attention of researchers.In this thesis,the preparation process,infrared radiation properties,temperature resistance,visible light compatibility of ZrB₂ films based on GH3536 high temperature alloy substrate are investigated,and the exploration was conducted on the corrosion resistance of ZrB₂ films.The main studies are as follows.1.Monolayer ZrB₂ films were prepared on alloy substrates by DC magnetron sputtering,and the effects of vacuum heat treatment and atmospheric heat treatment on the infrared emissivity properties of ZrB₂ films were investigated:the infared emissivity of ZrB₂ films prepared on alloy substrates had metal-like properties at room temperature,with an average emissivity of 0.279 in the 2-14μm band;due to the mismatch of thermal expansion coefficients between ZrB₂ and the substrate and the diffusion of the substrate elements,the emissivity deteriorates because of the large number of cracks and even partial peeling of the film surface after vacuum heat treatment at 1000°C for5-15 min.After heat treatment at 500°C for 10-20 h under atmospheric atmosphere,the reflectivity of the films in the visible band decreases and the adhesion is good,but the emissivity increases due to partial oxidation of ZrB₂,which cannot meet the requirements of high temperature and long time applications.2.The Al₂O₃ transition layer was introduced to investigate the infrared radiation properties,temperature resistance,visible light compatibility and corrosion resistance of Al₂O₃/ZrB₂ bilayer films.When the Al₂O₃ transition layer is 100 and 200 nm,the1000°C vacuum heat treatment can make the film crystallize and reduce the emissivity;meanwhile,the thicker the transition layer is,the stronger the blocking effect on the substrate elements and the less the influence of the substrate roughness on the surface morphology of the film;the temperature resistance of the film with the transition layer of 200 nm is better after the 500°C atmospheric heat treatment;under the influence of the surface roughness of the film,the visible reflectivity of the composite film decreased after annealing,with good visible light compatibility and good adhesion;the average infrared emissivity of 2-14μm remained stable after 960 h salt spray corrosion,and the electrochemical corrosion test showed that the corrosion resistance of the film remained almost unchanged after 960 h salt spray corrosion.