Effect of Emission Current on the Microstructure and Local Mechanical Response of EB-PVD Thermal Barrier Coatings

Electron beam physical vapour deposition (EB-PVD) is one of the most advanced technologies for manufacturing thermal barrier coatings (TBCs) with a columnar microstructure and excellent durability under high-temperature service conditions. This study investigates the relationship between electron beam emission current, deposition conditions, microstructure, and mechanical response of 7 wt.% yttria-stabilised zirconia (7YSZ) thermal barrier coatings deposited using an industrial-scale SMART COATER system. The coatings were characterised by microstructural analysis, ASTM C633 tensile testing, and Vickers indentation measurements. Increasing the emission current resulted in higher substrate temperatures, increased evaporation intensity, and a higher deposition rate, leading to thicker coatings with a progressively coarser columnar microstructure. The ASTM C633 testing resulted in cohesive failure within the adhesive layer, indicating that the measured tensile failure stresses provided only a lower bound for coating adhesion. Vickers indentation revealed clear through-thickness hardness variations and higher local hardness for coatings produced under higher-emission-current conditions. Overall, the results demonstrate systematic relationships between deposition conditions, columnar microstructure, and local Vickers hardness of the EB-PVD 7YSZ coatings.