The Numerical Simulation Research On Failure Factors Of Thermal Barrier Coatings

Thermal Barrier Coatings（TBCs） are used as thermal protection in airplanes and for powergeneration operate at extremely high temperature due to their conductivity, anticorrosion,antioxidation properties which maximize energy efficiency and prolong service life. The main factorsof premature spallation-failure are （1） multitudinous cavity in top ceramic coat;（2） the thermalexpansion mismatch stress among the coatings;（3） the undulate morphological of the interface;（4）increasing TGO in service processing. Thus deep study and analysis of the factors which lead to thecoating failure is extremely important. The content and result as follows:Firstly, the processing of plasma spray is simulating for optimize the process parameters inorder to improve the spreading properties of the coatings and reducing the porosity within the ceramiclayer. The Computational Fluid Dynamic software FLUENT is used to simulate the morphologicalchanges of single spray droplet in spray processing, and internal flow field in the droplet isinvestigated for understanding the laws and the nature of droplet spread. The effect of the dropletvelocity on the porosity and combine properties is analyzed. The degree of spread processing isdependent on velocity of droplet. With the velocity increaseing, the radius of spread is increasing, theroughness of interface is decreasing and the porosity of TBC is elevating. Preheating temperature caneffectively reduce the level of the interface stress, but the velocity of droplet play a slight role in theinterface stress.Secondly, the comparative analysis of the stress state between a typical double-coating andgradient coating, and the influence of the compositional exponent n of the gradient coating on stress isconsidered. While the compositional exponent n=1, the level of the stress is the best among theanalytical cases. On the base of the rational design of component, the influence of coatings thicknessis considered. The optimize result showed that the coating thickness d=0.55um, the combine propertyof the coating is excellent. Moreover, the influence of TGO is investigated. The simulate resultdemonstrated that the growth of TGO enhanced the level of the stress. It can be remedy bypre-prepared an Al₂O₃thin coating in the interface of TBC/BC to alleviate the stress.In addition, the influence of the interface morphology, the amplitude of morphology and thethickness of TGO in different amplitudes on stress of interface are studied. The result demonstratedthat the stress is dependent on the curvature of the interface morphology. With the roughness of theinterface is augment, not only the level of the stress is increasing but also the mechanical locking of interface is enhancing. The performance of the coatings is specific with difference condition.Morphology amplitude and the increasing TGO thickness can significantly promote the interfacestress.