Effect Of Thermal Barrier Coating Structure On Thermal Resistance Performance

The permissible temperature of the aero-engine hot end part is related to the thermal resistance of the thermal barrier coating on the surface of the aero engine,and it is greatly affected by the characteristics of the coating structure.However,the analysis of structural characteristics by previous generations has focused more on porosity,and the influence of pore shape and distribution has not been thoroughly considered.In this paper,the pore shape factor and distribution factor related to thermal conductivity are introduced to establish the relationship between the coating structure characteristics and thermal conductivity,and the effect of the coating structure on the thermal performance of the coating is quantitatively analyzed.Firstly,the pore-controllable thermal barrier coatings were prepared using a novel pore-making process.This process utilizes the sol-gel method to coat the surface of polyphenyl ester powder with"high temperature protective film"titanium oxide.The coated polyphenyl ester powders and yttria partially stabilized zirconia(YSZ)fine powders are agglomerated by spray granulation method to obtain final coating spray powders.The ceramic surface layer was prepared by plasma spraying method,and the porosity of the coating was controlled in four ranges of 2.5%,11.5%,24.4%,and 30.1%.Next,scanning electron microscopy(SEM)was used to analyze the cross-sectional morphology and pore structure of different coatings,the shape characteristics and distribution characteristics that have a great influence on the thermal conductivity are counted,including the pore aspect ratio,tilt angle,and the distance from the pore to the heat input surface of the coating.In this way,the shape thermal conductivity?_c and the distributed thermal conductivity?_d related to the thermal conductivity of the coating are defined,and the expression of the thermal conductivity regarding the pore structure is established.Then,the thermal conductivity of the coating at 100-900°C was measured by laser flash method,the specific values of the shape thermal conductivity parameters and the distributed thermal conductivity parameters in the thermal conductivity expression established in the previous section were obtained by fitting.The results show that the shape thermal conductivity?_c is 0.0287 W/(m?K)at 300°C,and the distributed thermal conductivity?_d is-2.783326 W/(m?K),the thermal conductivity of the coating decreases with increasing temperature,the shape thermal conductivity?_c and the distributed thermal conductivity?_d increase with increasing temperature.The shape thermal conductivity?_c at 900°C is 0.044 W/(m?K),which is increased by about53%;the distributed thermal conductivity?_d is-6.48126 W/(m?K),its absolute value increases by about 133%.It shows that the higher the temperature,the greater the influence of the pore shape and distribution on the thermal conductivity of the coating.Finally,thermal resistance tests under different temperature conditions were performed on the coatings with different pore structure characteristics.The results show that the thermal conductivity formula established in the previous section calculated that the thermal conductivity of the coating made of small particle size of PHB as pore former at 500°C.decreased by 2.2%,and the corresponding temperature drop of thermal resistance increased by 38%.At 900°C,the thermal conductivity decreased by 3.1%and the temperature drop increased by 12.4%.When the porosity of the coating is similar,as the pore projection increases in the normal flow area of the heat flow and the average distance from the pore-to-heat input surface decreases,the effective thermal conductivity of the coating decreases and the thermal resistance increases.