Numerical Evaluation of Improvements in Thermal Barrier Coating Adhesion by Adoption of Plasma Treatment and Biomimicry

Thermal Barrier Coatings or TBCs for short, are an imperative part of the thermal protection system of expensive equipment and machinery in the automobile and aeronautics industries. However, the problem of adhesion has plagued the TBC field for years, leading to catastrophic failures in critical TBC systems. Efforts to chemically improve bond strength have not been entirely successful, so the other efficient way to do this would be some kind of mechanical interlocking that occurs at micro/nano scales. This work deals with the improvement of adhesion in TBC systems by numerical simulation and bench-marking of micro-geometric surface features that has been synthesized or reproduced in a laboratory environment through mechanical or electrochemical operations. For this, several geometries that benefit mechanical interlocking, and consequently improvements in mechanical ‘adhesion’ in TBCs have been compared. To simulate the mechanical and thermal loading on the micro geometries and to observe their effect, the commercial finite element software COMSOL was used. An analogy was drawn between the biological, Van der Waals dry adhesion mechanism in Gecko feet and that in the top surface of the thermally grown oxide (TGO) layer in TBC since the ‘mushroom head geometry’ in the Gecko feet provides improved adhesion (as much as 10 folds) compared to other geometries (spatular head, spherical head, or plain triangular crevices). An affordable synthesis process, termed “Electrolytic Plasma Processing (EPP)” for recreating this specific geometry, is also proposed and its utility briefly discussed.