Abstract
Gas turbine (GT) blades are exposed to high-temperature combustion gas that exceed the thermal resistance temperature of Ni-based superalloy. Therefore, the blade surface is coated by thermal barrier coating (TBC), which consist of two layers: a ceramic top coat (TC) and a bond coat (BC). The cyclic thermal loading in GT operation causes damage to the TC layer, such as cracking and delamination. Therefore, GT blades utilized in thermal power generation are periodically recoated to prevent such damage. However, recoating costs constantly, and it is required to extend the recoating period to reduce it. For this reason, advanced technology that enable nondestructive and simple deterioration diagnosis of damage to TBCs has been actively developed globally. In this study, we focused on the rebound-type hardness test, in which microspheres are impacted on the TBC surface, and attempted to relate the hardness value (Leeb hardness) to the damage of the TBC.
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