Microstructural and Mechanical Properties Changes of a NiCoCrAlY Bond Coat with Heat Exposure Time in Air Plasma‐Sprayed Y2O3–ZrO2 TBC Systems

Abstract

Changes in the microstructure and Young's modulus of NiCoCrAlY bond coat (BC) layer in a Y2O3 partially stabilized ZrO2 thermal barrier coating system exposed at 1423 K up to 100 h have been studied. Under the as‐sprayed condition, the BC layer consists of a fine mixture of β and γ′ phases. After heat exposure, the phases change in two different zones; in the zones adjacent to the TBC and substrate layers, a γ phase is present, and in the mid‐zone between the two interfaces, a mixture of β and γ phases is present. With an increase in exposure time, the BC microstructure transforms with time into a single γ phase. Young's modulus of the BC increases with increasing heat exposure time. In the as‐sprayed state, the global effective Young's modulus of the BC is originally 178 GPa and with an increase in exposure time changes to 182, 186, and 192 GPa after 10, 50, and 100 h of heat exposure time, respectively. This observation is explained by the change in the microstructure from the γ′ to the γ phase and the increase of existing γ phase, as the Young's modulus of the γ phase is higher than the β and γ′ phases.