Effect of substrate rotation on the microstructure of 8YSZ thermal barrier coatings by EB-PVD

Abstract

Thermal Barrier Coatings (TBCs) is an essential requirement to protect aero engines and gas turbines against high inlet gas temperatures. The microstructure plays an important role in governing the performance and thermal life cycle of the TBC structure. The TBC deposition process is carried using a combination of the Electron Beam Physical Vapor Deposition (EB-PVD) and Atmospheric Plasma Spray (APS) process. The microstructure obtained by EB-PVD represents columnar structure whereas APS represents splat layer structure. The combined deposition process is used to study the grain growth behavior which can affect the performance of the TBCs. The 8YSZ TBC was deposited by the in-house EB-PVD system onto the Ti-6Al-4V substrate with the NiCrAlY bond coat by the APS process. In this paper, the effect of substrate rotation on the microstructure of 8YSZ TBCs has been investigated and discussed in detail. The dissimilar grain growth behavior of the TBC was observed with the stationary and rotating substrate at 20 rpm for microstructural analysis. It was found that the stationary substrate with 8YSZ TBC has dense and fine grain growth behavior compared to a rotating substrate. In stationary condition, the substrate is always exposed to uniform deposition, therefore the grains with less shadow region is present which results in low porosity. Whereas, a substrate with rotation consists of distributed grains resulting in more shadow region contributing towards high porosity. Therefore, the substrate rotation affects the grain distribution resulting in the shadow region which leads to the formation of pores affecting the performance of TBCs.