NDE of degraded thermal barrier coating using impedance spectroscopy (2nd report- thickness evaluation of thermal barrier coating)

摘要

Application of a ceramic thermal barrier coating (TBC) to gas turbine blades has brought improvements in engine performance, durability, and fuel economy. Turbine blades with TBC are used in severe conditions of high temperature and long-termoperation, however, and damage and degradation such as reduced coating thickness, cracking, delamination, and spalling can be initiated in the TBC. Nondestructive evaluation (NDE) is an essential technique for use in the detection of damages anddegradation of TBC components. NDE of TBC damage and degradation can prevent accidents such as destruction of the turbine blades.In this report, the thickness reduction of the TBC is evaluated by impedance spectroscopy (IS). Yttria stabilized zirconia (YSZ) has been a popular TBC material, therefore, impedance measurements were performed on sintered YSZ and plasma sprayed YSZ. Theimpedance behavior of YSZ was found to be remarkably changed with variation in TBC thickness. This thickness can be evaluated by impedance measurements, and the thickness of sintered and plasma sprayed YSZ were determined to within 15% and 25% error,respectively, at a constant temperature.