By applying a small punch testing technique, it has been previously shown that near-surface aluminized CoCrAlY coatings of unused advanced gas turbine blades had very low ductility due to the formation of Al and Cr rich phases, compared to internal and near-interface regions. Thus, it is important to examine how in-service operation affects the mechanical properties of the internal, near-interface coatings and substrates to maintain the integrity of gas turbines. This study attempts to compare the effects of in-service operation for 20,000 h under combustion of liquefied natural gas and thermal ageing in air. The in-service operation led to a larger ductility loss in concave coatings near the tailing edge, although the ductility slightly improved above testing temperature at 950 °C. Substrate used in-service had lower ductility at 950 °C than the used concave coatings. The ductility of used internal coatings depended on the blade location. In convex coatings near the leading edge, in-service degradation was not significant and the ductility was about two-fold greater than in the thermally aged blade. The in-service degradation mechanism of the aluminized CoCrAlY coatings is discussed in light of the operating temperature distribution and microstructural evolution.

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