Analysis on tenon tooth cracks of a second stage high-pressure turbine blade

• Recrystallization, phases, grain boundaries, geometrically necessary dislocation and strain contouring of the fifth tenon tooth root surface were analyzed via EBSD technique. • The operating temperature and stress of the fifth tenon tooth root were not the primary causes of crack initiation based on the finite element analysis. • The formation of the white layer and fine secondary γ′ phases near the cracks along the carbides ascribed to grinding burn. Several cracks were observed on the fifth tenon tooth root of some second stage high pressure turbine blades of an aero-engine after ground test run. Surface and sectional morphologies of cracks, recrystallization and microstructure of the near-surface were utilized to explore surface integrity of the tenon tooth root. Besides, the finite element analysis was carried out to estimate the static strength and temperature field of the turbine blade. The results showed that most of the cracks were along the near-surface carbides, where undergone grinding burn with the formation of the white layer and fine secondary γ′ phases, and then cracks fatigue propagated during operating. Some cracks above the microporosities were ascribed to the local stress concentration when contacting with the grinding wheel during the creep feed grinding. The recrystallization occurred on the tenon teeth surface during annealing at 1000℃ for four hours after grinding, and related cracks were not observed in the recrystallized fine grains layer during operating.