Analysis of the Stress Distribution in Thermal Barrier Coatings

This paper investigates the state of stress induced by oxidation of a typical plasma sprayed thermal barrier coating. At high temperature a thin layer of thermally grown oxide forms in the barrier, and growth with time. Observation of specimens after laboratory tests gave important information about the shape of the oxide layer and about the oxidation law. The oxide is the main responsible for the stress in the thermal barrier coating. A finite element model of a TBC has been developed with temperature-depending material properties, simulating the strain due to lateral growth of the oxide and considering the sintering of the ceramic materials. Time dependent behavior, such as oxide creep, has been taken into account with a simplified model. Simulation has been done for both isothermal ageing and thermal cycles. The location of the maximum stresses in the model are consistent with the location of crack propagation observed in the experimental tests.