Finite Elemente Simulation gemessener Eigenspannungen in plasmagespritzten Mehrschichtsystemen

Plasma sprayed multilayer systems are used for high temperature protection. System functionality is mostly influenced by residual stresses originating in the plasma spraying process. The aim of this work was the prediction of these residual stresses. A single layer model was further developed to the analytic stress model for multilayer systems (ASM). The calculation is based on the infinite plate. Simultaneously the finite element stress model (FSM) was designed. To verify both models residual stresses in dependence on different coating parameters were measured by X-ray diffraction and compared with calculated values. The multilayer system relevant to fusion technology consists of boron carbide top coating with copper interlayer applied on substrate stainless steel 316L. The system was studied concerning the processing parameters coating temperature, top coating thickness, interlayer thickness and substrate diameter. The experimentally detected residual stress dependence on coating temperature could not be followed by the analytic stress model. It is unsuitable for describing systems with metallic interlayers. In contrast the finite element stress model showed good agreement with measured values. Accordingly all further simulations were carried out with this stress model. The model qualification was also proved by the variation of top coating thickness and interlayer thickness. All calculated results with the FSM were achieved without the explicite simulation of the coating construction . Only the residual stresses which occure during cooling of the total multilayer system from coating temperature to room temperature were calculated. This simplification could be used because the system was almost stressfree after spraying of the copper interlayer. The second studied multilayer system is relevant to thermal barrier coatings for application in stationary gas turbines. It consists of YSZ top coating with MCrAIY interlayer applied on Ni based superalloy as substrate. Residual stresses in the YSZ top coating simulated without coating construction did not correspond with measured values concerning sign. The calculation of the system of MCrAIY coating applied on superalloy showed very high tensile stresses in the coating. Therefore a simplification analogous to the first multilayer system was impossible. The explicite simulation of coating construction resulted in calculated tensile stresses in the YSZ top coating analogous to the measurement. But the amount of calculated values was evidently too high. The consideration of time dependent material behaviour with purpose of stress relaxation as for example creep may improve these results