Reason for Gracks of Inner Nozzle

Cracks appeared in the heat affected zone of the surface tack welding spot and roll welding spot of a GH536 alloyed inner nozzle of a certain aircraft after working for 22 h. The reason for cracks was analyzed by fracture morphology and microstructure observation and chemical composition test. The results show that the cracks on the inner nozzle were fatigue cracks initiated under a relatively large stress and propagated under a relatively small stress. The argon arc welding positioning did not meet the process requirements of the inner nozzle, and the tack welding spots were not removed. During the fatigue loading, there was stress concentration in the heat affected zone of the tack welding spot and the subsequent roll welding spot, leading to initiation of fatigue cracks.