Microstructure and texture of EB-PVD TBCs grown under different rotation modes

Abstract

The role of vapor incidence pattern (VIP) on the microstructure and texture of thermal barrier coatings (TBCs) produced by electron-beam physical vapor deposition (EB-PVD) is examined. Two distinct VIPs are induced by proper design of the substrate rotation mode. One is the sunrise–sunset pattern typical of conventional deposition on the curved face of a rotating cylinder (mode A), and the other is a conical pattern resulting when deposition is done on the cylinder base at an offset distance from the plume axis (mode P). These geometries afford fundamental insight on the processes of microstructure and texture evolution and also have practical implications to the variability of properties that may be expected between the body and platform regions of a turbine airfoil. Comparable deposition rates and thickness uniformity can be achieved by proper selection of the experimental geometry. Both coatings exhibit the typical 〈100〉 texture normal to the substrate, but mode A also yields a preferred in-plane orientation which is absent in mode P. The ensuing differences in column packing and tip shadowing yield lower densities and larger pipe-like inter-columnar voids in mode P. The absence of an in-plane evolutionary selection mechanism in the latter also leads to narrower columns than in mode A.