Study On Deposition Mechanism And Performance Of YSZ Coating Based On Plasma Spraying Technology

With the continuous increase in flight speed of modern aircraft,the application temperature of hot end components represented by tail nozzles is also increasing,resulting in more obvious infrared radiation characteristics,thereby increasing the risk of aircraft being recognized and tracked by infrared detectors.In order to improve the survival and combat capabilities of aircraft,there is an urgent demand for the development of new high-temperature resistant infrared stealth materials.Metal oxide ceramics,represented by yttrium stabilized zirconia（YSZ）,have high ion conductivity and low thermal conductivity at high temperatures,and are expected to become a new generation of high-temperature resistant infrared stealth materials.In response to the urgent need for high-temperature infrared stealth of future weapons and equipment,this dissertation takes high-temperature resistant metal oxide YSZ coatings as the research object,and systematically studies the deposition mechanism and infrared radiation characteristics of YSZ coatings based on plasma spray physical vapor deposition（PS-PVD）and atmospheric plasma spray（APS）technologies.The effects of microstructure and crystal structure on the infrared emissivity of YSZ coatings were discussed in detail,and the performance of YSZ coatings in high temperature environments was deeply explored.The formation reason and control mechanism of YSZ emissivity were explained based on lattice vibration theory and optical theory.The specific research content and conclusions are as follows:1.The deposition mechanism and infrared radiation performance of YSZ coating prepared by PS-PVD were studied.The temperature field,velocity field,and pressure field in the PS-PVD plasma jet were simulated,explaining the process and reasons for the formation of YSZ feather columnar crystal coating.The microstructure,elemental valence states,growth orientation,and microhardness of different parts of the coating were discussed.The relationship between the microstructure and crystal structure and the infrared radiation performance of YSZ coating was established.It was found that increasing the gap between the columnar crystals of the coating feather would improve the probability of the coating absorbing infrared radiation.Therefore,the larger the columnar crystal gap,the higher the infrared emissivity of the coating.As the heat treatment temperature increases to 1200℃,the gap between the feather columnar crystals of the YSZ coating decreases,the crystallinity and grain size increase,weakens the scattering effect at grain boundaries,and the emissivity of 3-5μm decreased from 0.73 to0.58.2.YSZ coatings were prepared on alloy substrates using APS technology,and the effects of microstructure and crystal structure on the infrared radiation characteristics of YSZ coatings were systematically studied.The experiment found that the surface roughness,porosity,and crystallinity of the coating can all affect the infrared radiation performance of the coating.After plasma surface treatment,the surface roughness of the YSZ coating increased from 10.5μm dropped to 2.1μm,and the coating of the average emissivity of the 3-5μm is reduced from 0.54 to 0.43.Due to the enhancement of the scattering effect of the coating on infrared light by pores,as the spraying power of APS decreases,the porosity inside the coating increases from 9%to 19%,the coating of the average emissivity of the 3-5μm band decreased from 0.54 to 0.44.In addition,the increase of porosity reduces the average free path of phonons,and the thermal conductivity of the coating decreased from 2.773 W/（m*K）to 1.926 W/（m*K）.With the increase of heat treatment temperature from room temperature to 1200℃,although the porosity of the coating decreases,the conductivity of the coating increases due to the increase in grain size,resulting in the coating of the average emissivity of the 3-5μm band is reduced from 0.44 to 0.33.The infrared emissivity of YSZ coating prepared by APS and PS-PVD were compared.The results showed that the"cauliflower head"structure and the"gully like"holes would provide a transmission channel for infrared radiation,increasing the absorption of infrared radiation by the coating,while the circular holes in the layered structure coating would enhance the backscattering energy of the coating and reduce infrared absorption,Therefore,the infrared emissivity of the layered porous structure coating prepared by APS is significantly lower than that of the feather columnar structure coating prepared by PS-PVD.3.A systematic study was conducted on the performance and application of YSZ coatings prepared based on APS technology in high-temperature thermal environments.The physical mechanism of the high temperature infrared low emissivity characteristics of YSZ coating is clarified.The increase in temperature caused an increase in thermal defects and carrier concentration in YSZ coatings,resulting in an increase in electrical conductivity and a decrease in infrared emissivity of the coatings,and the infrared emissivity of YSZ coating in 3-5μm waveband was 0.321 at 800℃,which suggested that YSZ coatings has excellent high temperature infrared low emissivity characteristics.The thermal conductivity and thermal insulation performance of YSZ coating at high temperature were studied.With the test temperature rising from room temperature to1200℃,the average free path of phonons decreased due to the intensification of phonon collision inside the coating,and the thermal conductivity of YSZ coating decreased from1.926（W/（m*K））to 1.402（W/（m*K））.When the aircraft surface temperature is 800℃and 1200℃,applying YSZ coating can reduce the target surface temperature by about300℃and 400℃,respectively,and according to the infrared stealth principle,in the 3-5μm waveband,applying YSZ coating can reduce the detection distance of the target aircraft by 123 km and 174 km,respectively,with an infrared stealth efficiency of over50%.4.Further regulation of the infrared emissivity of YSZ is achieved by combining and doping different metal oxides.According to the lattice vibration theory and dispersion formula,the relationship between the resonance frequency of metal oxides and optical properties has been revealed.By combining different amounts of Ti O₂,the resonance frequency of YSZ has been effectively regulated,resulting in a gradual shift of the Christiansen wavelength of YSZ towards the short wavelength direction,reducing the infrared emissivity of YSZ in the 8-14μm band.By doping different amounts of MgO in YSZ,the extinction coefficient of YSZ is reduced to a certain extent,while doping effectively increases the concentration of oxygen vacancies in YSZ,which increases the conductivity of the coating and further reduces the infrared emissivity;The optimal doping content of MgO is 5mol%,YSZ of the emissivity of the 2-14μm band is reduced from 0.336 to 0.296,realizing effective regulation of emissivity.In this dissertation,the deposition mechanism and performance of YSZ coating prepared by PS-PVD and APS plasma spraying technologies were investigated in detail,and the influence of microscopic morphology,crystal structure and composition on the infrared radiation performance of the coating was discussed in depth,which provides theoretical support and experimental basis for the application of YSZ coating in the field of high-temperature infrared stealth materials.