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Evaluation of Tensile Properties and Microstructure of a Scraped Gas Turbine Blade using Miniature Specimens

A gas turbine (GT) blade is a key hot-pass component for advanced GT engines, and should have stable properties under extreme conditions of 1,350°C and 3,600rpm, etc. The GT blade, after operating with nearly 800 equivalent start-stops (ES) or 24,000 equivalent operation hours (EOH), should be replaced due to degradation of properties and microstructure, particularly, the formation of cracks in the airfoil tip and platform region. To date, the assessment of materials, prototype blade, etc, has been extensively studied in a laboratory simulated environment; however, evaluation of the full-scale blades in a service environment has been rarely reported. Here, the properties and microstructures of an F-class GT first stage blade, with a service history of 800ES were investigated. The results showed decreasing tensile properties at the airfoil part due to its higher temperature exposure. The microstructural characterization results revealed that the finer grain size and dendrite interfaces facilitated the formation of Cr-enriched M23C6 along grain boundaries, as well as the spherical γ' in the airfoil part, resulting in a decrease in tensile properties. The results obtained here provide precious background for assessing the serviced blade and developing advanced blades.