Sensitivity analysis of EB-PVD thermal barrier coatings for aerospace applications

Abstract

Thermal Barrier Coatings (TBC’s) created by Electron Beam Physical Vapour Deposition (EB-PVD) are widely used in the aerospace industry. Advancements in the field however are hindered by the cost and time required for research and development. Hence, there exists a need for a more comprehensive understanding of coating parameter interactions to better predict response values without the need for extensive pre-production testing.

This thesis seeks to provide a response surface for EB-PVD coatings, by investigating the following EB- PVD independent input variables: electron beam emission current, gas ratio, vacuum pressure, substrate temperature, roughness and process time in order to generate a predictive statistical model. Output variables were numerous, however emphasis was placed on: TBC coating thickness and density of columns generated during the process. It is impossible to select an “optimum process recipe”; rather, there exists many optimal combinations suited to specific coating structure and its application. Therein lies the need for this model, able to predict TBC properties according to input variables.

Using ALD’s Smart Coater (ALD Vacuum Technologies GmbH), a ceramic top coat (Yttria partially stabilized zirconia, YPSZ, ZrO2-7%Y2O3) was deposited onto 40x30x5mm Inconel 617 samples with NiAl bond coat. These samples were subsequently tested to determine coating properties. The research will show that the complex nature of EB-PVD TBCs may be simplified, at least to a certain degree through a statistical analysis of the interactions between process variables.