With the application of nickel alloy electron beam welding in industry,especially in critical long service equipment such as aircraft engine and gas turbines etc.,it is necessary to systematically analyze and study the high cycle fatigue properties and fracture mechanism of nickel alloy electron beam welding joint.Fatigue tests were carried out using the rotary bending high cycle fatigue testing machine.The stress-life (S-N) curves and fatigue fracture of the base metal and welded joints were obtained from experiments.Then,the fatigue fracture surfaces were examined by scanning electron microscope (SEM).The fatigue crack initiation and extension zones of the base metal and welded joints under different stress amplitude were analyzed and determined,in which the crack initiation location was affected by the stress amplitude.Finally,the effect of the location and size of microcracks on the fatigue properties of the welded joint was discussed by the finite element method (FEM).The experimental and simulation results showed that:the stress-life (S-N) curves distribution trend of the base metal and welded joints is consistent,and fatigue strength of the welded joint is lower than the base metal,which there is small difference nearby the 107cycle.With the high stress amplitude (low cycle fatigue life stage),fatigue crack initiates from multiple point at the surface for base metal and welded joints.The fracture position of welded joints is located in the weld fusion zone and heat affected zone.The fatigue crack initiation transforms from surface to subsurface in the low stress amplitude (high cycle fatigue stage).The fatigue fracture of the welded joints is located in the heat affected zone and base metal near the heat affected zone.The existence of microcracks is beneficial to the propagation of crack by FEM.Under the tensile stress,the transverse microcracks are better than the longitudinal crack to propagate along the stress direction.With the increase of the microcrack size,the microcracks are easier to cross each other and form longer cracks,to reduce the fatigue performance.The results also showed that the electron beam welding only affects the fatigue strength of the material,the fatigue failure property and the fatigue crack initiation position is the transcrystalline cleavage fracture and directly affected by the stress amplitude,respectively,which is consistent with the base metal.
