Failure Mechanisms of Thermal Barrier Coatings at High Temperature

Abstract

Thermal barrier coatings (TBCs) are widely used in turbine engines. They are regarded as one of the most successful innovations and applications of coatings in industry. Thermal barrier system comprise thermally insulating materials having sufficient thickness and durability that they can sustain an appreciable temperature difference between the load bearing alloy and the coating surface. TBC exhibit multiple failure modes. Among them, the Foreign Object Damage (FOD) and mechanical erosion are the most prevalent failure modes of TBC at high temperature. In this study, based on a new scaling analysis of impact mechanics, FOD and erosion of TBCs are analyzed by using the finite element method. Impact and material variables are grouped into the smallest possible parameter set to provide explicit results. Microstructural effects are factored into the approach. Three different domains have been explored governed by particle size, velocity, temperature and TBC composition. Numerical simulations show that crack initiation is activated by transient stresses and delamination is governed by residual stresses. The transient stresses occurring near the free surface lead to crack initiation and material removal. Failure criterions are derived which provide useful insights on how to improve FOD and erosion resistances.