Study On The Preparation And Properties Of Thermal Barrier Coatings With Low Thermal Conductivity For Ultra-high Temperature Applications

Thermal barrier coating is a kind of ceramic material deposited on the surface of superalloy substrate to protect the substrate material from high temperature erosion.Because of its good high temperature resistance,low thermal conductivity,and the thermal expansion performance matching with the substrate,it is widely used on the surface of high temperature parts such as aviation engine combustion chamber,which becomes an irreplaceable insulation material for modern aviation equipment(combustion chamber,airin duct,tailpipe,etc.).At present,yttria partially stabilized zirconia(YSZ)is mainly used in practice,while the long-term service temperature of YSZ ceramic material cannot exceed 1200?.In the field of aeronautics and astronautics,with the appearance and development of hypersonic vehicle,the surface temperature of its high-temperature components has far exceeded 1200?,the demand is close to 2300?,and the surface temperature of the coating has reached more than 1600?.The existing thermal barrier coating can no longer meet the ultra-high temperature demand of the weapon model,so it is necessary to develop a new type of thermal barrier coating with low thermal conductivity under ultra-high temperature conditions.Therefore,new ceramic coatings with low thermal conductivity,high thermal expansion coefficient,high temperature phase stability,low sintering rate and high temperature corrosion resistance have become the research focus and hot spot.In order to meet the urgent needs of the development of aerospace industry,new type of thermal barrier coatings materials of M0.02Gd0.025Yb0.025Y0.05Zr0.88O1.94(M=Dy,Er,Eu,Sm,Nd)and N0.02Dy0.02Gd0.025Yb0.025Y0.05Zr0.86Ox(N=Ti,Mn,Si,Mg,Cr)with low thermal conductivity for ultra-high temperature were designed and synthesized by using zirconia with good comprehensive properties as the main material and doping rare earth and non rare earth elements as the solid solution system The crystal structure and coating thermodynamic properties of the multi-doping system powders and coatings are systematically studied.The influences of ion radius and valences on the coating performance are studied.At the same time,combined with modern computer simulation technology,the temperature field change,thermal stress change and deformation of the coating in the ablation process were simulated to predict the most likely failure position of the coating.In order to further improve the performance of the coating,the pore structures of the coating were designed to improve the problem of thermal stress concentration of the coatings,and extend the service life of the thermal barrier coating,and improve the thermal insulation performance of the coating,and reduce the temperature to the base of the superalloy.The specific research contents and results are as follows:(1)Preparation and properties of binary ion doped(La1-xScx)2Zr2O7 powders and coatingsThe La2Zr2O7 coating with low thermal conductivity was modified by doping new elements.The effects of different content of Sc3+ ions on the thermal properties of the coating were studied by doping near rare earth Sc3+ions with small radius.Scandium ion doping can reduce the thermal conductivity of lanthanum zirconate coating.When the content of Sc3+ is 0.1,the thermal conductivity of the coating is the lowest.The thermal conductivity of the Sc0.1 coating is 8.8%lower than that of the single La2Zr2O7 coating at 1600?.(2)Preparation and properties of ceramic powder and coating of M0.02Gd0.025Yb0.025Y0.05Zr0.88O1.94A new type of quaternary M0.02Gd0.025Yb0.025Y0.05Zr0.88O1.94 ceramic powders was prepared by high temperature solid-state method.Moreover,the powder preparation process is simple,high output and stable performance,which is suitable for large-scale batch production The NiCoCrAlY metal bonding layer with thickness of about 100 ?m was prepared on the surface of Superalloy(GH4169)substrate by air plasma spraying,and the ceramic coating was prepared on the surface of the bonding layer.Compared with the YSZ coating,the new ultra-high temperature thermal barrier coating has better high temperature ablation resistance and lower thermal conductivity,which can be used as the ultra-high temperature thermal barrier coatings for aeroengine in the future.(3)Study on the preparation and properties of five element N0.02Dy0.02Gd0.025Yb0.025Y0.05Zr0.86 Ox doped modified ceramic powders and coatingsIn view of the poor thermal shock resistance of the above-mentioned four elements zirconia based thermal barrier coating,we further modified it by doping non rare earth oxides with low melting point.The modified five component ceramic coating prepared by solid-phase method not only keeps the advantages of the four components coating,but also improves the thermal shock resistance of the coating.Reducing the thermal conductivity of the coating,especially at 1600?,its thermal conductivity is 0.974 W/(m·K),which is 44.3%lower than the traditional YSZ(1.749 W/(m·K))coating.Therefore,the modified new thermal barrier coating is an ideal choice for hot end components of aviation.(4)Pore structures design and thermodynamic properties of thermal barrier coatingsThe physical pore structure of the coating is designed on the basis of the existing coating.The theoretical calculation can optimize the coating pore structure with the lowest cost and the fastest speed,which will play a theoretical guiding role in the future coating structure design optimization.The results show that the coating with semicircular pore structure has the minimum strain,the best heat insulation performance and the minimum thermal stress.This is the first attempt and report to improve the coating performance by improving the physical pore structure of the coating.