Residual Stresses of Eb-pvd Thermal Barrier Coatings Exposed to High Temperature

The substrate material was nickel-based superalloy (In738LC), and CoNiCrAlY was pressureless plasma-sprayed on the substrate as the bond coating. As the top coating, zirconia with 4 mol% yttria was electron beam-physical vapor deposited (EB-PVD) on the rotating substrate. The rotation speeds in the EB-PVD process were 5, 10 and 20rpm. The specimens were exposed to 1273K in air atmosphere for 200h. The in-plane residual stress was measured by a conventional X-ray method, and the out-of-plane residual strain was measured by the strain scanning method using hard synchrotron X-rays. For the specimens rotated at 5 and 10rpm, in-plane compressive residual stresses were relieved by the high temperature exposure. For the specimen rotated at 20rpm, the in-plane residual stress did not change by the high temperature exposure, because it was very small before the exposure. The in-plane residual stress near the interface was a large compression for all cased examined. For the specimens rotated at 5 and 10rpm, out-of-plane stresses were small near the coating surface but became compression near the interface. Both in-plane and out-of-plane residual stresses of the specimen rotated at 20rpm were very small. From a viewpoint of reduction of the residual stress, the rotation speed of 20rpm was excellent. The EB-PVD TBC was made by columnar structure, which was composed of core and peripheral parts. The peripheral part had feather-like structure. According to the observation with scanning electron microscopy, the feather-like structure cohered and shrank after the high temperature exposure. The volume reduction of the columnar structure relieved the in-plane residual stresses. INTRODUCTION Electron beam-physical vapor deposited (EB-PVD) thermal barrier coating (TBC) is one of the key technologies in gas turbine engines in the future. The EB-PVD TBC made on a rotating substrate has a unique columnar structure with the feather-like peripheral part. The EB-PVD TBC has a large compressive residual stress [1], but it can be reduced by the rotation method [2]. According to our previous studies, the in-plane compressive residual stresses decreased with the increase in the rotation speed, and the out-of-plane residual stress was small [1,2]. Therefore, the EB-PVD with the rotation method is endowed with excellent 537 Copyright ©JCPDS-International Centre for Diffraction Data 2009 ISSN 1097-0002