Internal Stress in EB-PVD Thermal Barrier Coatings under Thermal Cycle
Kenji SUZUKI and Takahisa SHOBU
Abstract:As the top coating, zirconia with 4 mol% yittria was electron beam-physical vapor deposited (EB-PVD) on the bond coating of CoNiCrAlY. The substrates were rotated during EB-PVD process and the rotation speeds were 5 (R5) and 10 rpm (R10). The thickness of the top coating was 0.12 mm. In order to investigate the change of the internal stress in the top coating by a thermal cycle, the specimen was heated from a room temperature to 1273K, the internal stress was measured in-situ by the strain scanning method with hard synchrotron X-rays at each temperature step. For the specimen R5. The internal stress increased from about -100 MPa to about 100 MPa with the increase in temperature, then the stress relaxation of the top coating occurred over 1073 K. For the specimen R10, the internal stress did not show a tension in the heating process, it was caused by the separation between columnar structure. In the cooling process, the internal stress decreased, however, the change rate of the internal stress was small as compared with the heating process. This was caused by sinterring of the feather-like structure. Key Words:Thermal barrier coating, EB-PVD, X-Ray stress measurement, thermal cycle, Synchrotron, Zirconia