Abstract: A blade broke from the tenon. Macroscopic inspection, microscopic inspection, metallographic structure and hardness inspection were carried out on the blade and its corresponding mortise and groove. The results showed that there were no abnormalities in the blade material and metallographic structure, and the hardness met the requirements. The fracture nature of the blade was high-cycle fatigue, with multiple fatigue zones, and the source area was a short-term source. The initiation of cracks was related to fretting damage on the side of the tenon; The silver layer near the edge of the mating surface of the blade tenon and the mortise is incomplete, there is residual sand on the surface of the metal substrate, and the tenon and the mortise are tightly fitted. These factors will deteriorate the surface contact state and cause local fretting damage.