The Research Of The Thermal Shock Resistance Of YSZ Active Diffusion Barrier Layer

Thermal barrier coatings, coated on aircraft engine surface, have excellent high-temperature protection, but it will cause element-interdiffusion between bond coat and matrix during long-time high-temperature service, resulting in degradation of coating performance and loss of mechanical properties of matrix. After a large number of studies, researchers found that diffusion barrier layer is an effective way to prevent element- interdiffusion between bond coat and matrix. However, the research on the thermal shock resistance of diffusion barrier layer is limited. Therefore, the research contents and results in this paper are as follows:1) In order to study the thermal shock resistance of diffusion barrier layer, samples were firstly heat up from 25 degrees Celsius to 900 degrees Celsius in 2 minutes, and then hold the temperature for 5 minutes and finally water-cooled. The influence of interface morphology and texture of activated diffusion barrier layer on its thermal shock lifetime is studied by changing the surface roughness of the substrate and preparation process. Experimental results shown that too rough or smooth surface is harmful to the thermal shock lifetime of diffusion barrier layer. Moreover, the texture of ZrO2 pioneer layer also has a big impact on the thermal shock resistance of the diffusion barrier system.2) The influence of thickness and interface morphology of diffusion barrier on internal stress distribution and stress changes in diffusion barrier system at instantaneous moment of temperature shock was studied via finite element analysis software ANSYS workbench. Simulation results shown that the thickness of Al2O3 layer and rich Zr layer has certain influence on the thermal stress value. And the influence of the ceramic layer is bigger than the metal layer as the young’s modulus of ceramic layer is 4 to 5 times higher than metal layer. When a larger temperature gradient existed in active diffusion barrier system, both the mismatch on thermal-physical properties and structural constraints between the metal and ceramic layer will cause stress concentration in diffusion barrier layer. And thermal stress cannot be weakened through plastic deformation due to the poor ductility of ceramic, thus, Al2O3 layer is a weak area in diffusion barrier system.3) The stress level in the "sandwich" structure of diffusion barrier, stress distribution and stress changes after several repeated thermal shock were studied by ABAQUS FEA software. In addition, the effects of the interface morphology on its internal stress distribution and the stress changes were emphatically analyzed. Results shown that, there are serious stress concentrations of S11, S22 and S12 at the outer edge of these two type. And the existence of singular interface lead to stress concentration of S22 and S12 in Al2O3 layer. And withal, the peak-value has major impact on the fluctuations of S11 and S22 stress in diffusion barrier system(particularly in Al2O3 layer). Besides, the instability of diffusion barrier increases with the heighting of peak. The result indicated that the better peak value is 1-3 μm.