Numerical Simulation Of Interface Asperity And Residual Stress In Thermal Barrier Coatings

Thermal barrier coatings are the heat insulation ceramic coats that were spread on the surface of metal substrate to utilize the qualities of ceramic materials , low heat conductance,resisting oxidation and be able to bear heat impact . It can improve the working temperature of metal substrate and prevent the transfer of heat from the exterior environment to metal substrate. Thermal barrier coatings have a wide application foreground in national defense and civilian industry .How to improve the performance of thermal barrier coatings and prolong its employing life are the hot spot of current research .It can be made by Plasma-Spraying, Electron Beamphysical Vapor Depositing and Laser cladding, etc .A typical thermal barrier coatings system consists of an oxidation –resistant metallic bond coat overlaid by a porous thermally-insulating ceramic coating. Both during the thermal cycles and during the plasma-spray deposition, the thermal stress that developed in the coating system due to thermal expansion differences in the interface can induce progressive fracture and eventual spallation of the ceramic coating along the interface .So how to strengthen the bonding of the coatings is a key of the life of TBC. In practice, interface roughening is an effective method to strengthen the bonding of the coatings and an effective method to improve the employing life of thermal barrier coatings. But the resultant interfacial asperities modify the residual stress in the system. For a flat interface, the principle residual stress is parallel to the interface, as the stress normal to the interface is zero. However, the tensile residual stress normal to the interface becomes nonzero, when the interface has the required interlocking morphology. and high tensile stress is thought as a major factor of spallation. It means the roughening of interface that strengthens the bonding of the coatings may introduce the negative factor on the life of TBC system simultaneously and immoderate roughening will do harm to interface and reduce the life of TBCs. So it is necessary to investigate the effect of interface topography on the stress in TBC. In this paper, our study object is thermal barrier coatings made by Plasma-Spraying, simulating the microstructure model by ANSYS, calculating the residual stresses in the coating system during cooling of heat cycles, researching the relationship between the residual stress and the interface asperities, comparing the distribution of the residual stress in the ceramic coat near the interface in different interface asperity, getting the distribution disciplinarian of the residual stress in the ceramic coat near the interface: The stress in the ceramic coat get obvious change along the anomalistic interface ,interface asperities have a remarkable influence on the qualities,distribution and magnitudes of residual stress near the interface in the ceramic coat; The sharp corner of interface (the break of interface geometry) can result in the break of the interfacial thermal residual stresses, the former is higher, so is the latter. In the case of wiping off the influence of sharp corner, a logical choice to reduce the stress would be to eliminate or reduce the convex asperities. Effect of interface asperity dimension on the tensile stress in the ceramic coat was researched in the paper too, that come to these conclusion (:1)The tensile stress normal to the interface and the compressive stress parallel to the interface in the ceramic coat increase with the curvature of interface asperity and the variety of curvature of interface asperity have a more influence on the tensile stress σy;(2)The tensile stress normal to the interface and the compressive stress parallel to the interface in the ceramic coat increase with the height of interface asperity. But the effect of the height of interface asperity on the tensile stress is not distinct;(3)The interval of asperities have a influence on the tensile stress normal to the interface and the compressive stress parallel to the interface in the ceramic coat. In the convex asperities, the tensile stressσy and the compressive stress σx increase with the interval of asperity; In the concave asperities, the tensile stressσy and the compressive stress σx decrease with the interval of asperity,and the variety of...