Abstract：Gas turbine blades operate under severe conditions including high temperature, complex stresses, oxidation, corrosion, and cyclic loading. Local crack initiation and growth can therefore degrade structural integrity and service reliability. However, standard fracture toughness specimens are difficult to prepare from blade materials because blades are thin-walled, geometrically complex, and limited in sampling volume. Different blade regions may also exhibit distinct microstructures and local mechanical responses. A miniature-specimen-based approach is thus needed for local fracture toughness evaluation. In this study, an RA-series nickel-based superalloy blade was investigated. Specimens were extracted from the blade airfoil and blade root. Metallographic observations were first conducted to characterize regional microstructural features. Small rectangular tensile specimens were then tested at room temperature and 900 °C to evaluate local tensile behavior without a macroscopic crack. Mini-SEB specimens were machined from the same regions to assess fracture behavior under cracked conditions. Fatigue pre-cracking was introduced under constant ΔK control. Fracture toughness tests were performed under displacement control, and the J–Δa curves and the conditional initiation toughness JQ0.2BL were determined using the normalization procedure recommended in GB/T 21143-2014. Fracture surfaces were further examined by macroscopic observation and scanning electron microscopy. The results show clear regional dependence of both tensile properties and fracture resistance. At room temperature, the blade root exhibits a higher yield strength, whereas the blade airfoil shows a higher ultimate tensile strength and larger fracture strain. At 900 °C, this trend reverses, and the blade root becomes superior in both strength and ductility. For both regions, the J–Δa curves at 900 °C lie above those at room temperature, indicating improved crack-growth resistance at elevated temperature. The average JQ0.2BL of the blade airfoil increases from 70.65 to 103.78 MPa·mm, while that of the blade root increases from 36.78 to 145.53 MPa·mm. All specimens show ductile fracture characteristics. These results demonstrate that Mini-SEB testing can provide reliable local fracture toughness parameters for gas turbine blades under restricted sampling conditions and support local structural integrity assessment at representative service temperatures.
2026, Vol. 47 
