Micro-vibration Fatigue Failure Analysis Of TC4 And Welded Joints Of Micro-plasma Welding

Fatigue properties of TC4 plate and its welded joint of micro plasma welding are represented in this paper. Firstly, the relationship between amplitude and life cycle of specimen is found; another test is planned to combine amplitude and strain; the stress is corrected by Abaqus simulation; S-N curve of vibration fatigue of TC4 is drawn by corrected stress, containing low-cycle, high-cycle and very high-cycle; the crack growth rate of rapid propagation area is recorded; the vibration fatigue limit of TC4 plate and its blade are compared; the number of vibration fatigue limit and rotational bending fatigue of TC4 are contrasted. Then, the fatigue fracture morphology is analyzed; relationship between number of crack and stress was found; the crack growth rates of stable propagation area under different stress level are calculated by the size of fatigue striation. After that, microscopic observation, mechanical properties, micro-hardness test and vibration fatigue test of welded joint through micro plasma welding are completed; relationship between stress level and disable position is found; relationship between life cycle of different areas and the base metal is found. At last, fatigue fracture morphology of welded joint is analyzed, failure mechanism of different area is determined; influence of depression and chain porosity on initiation and propagation of cracks is discussed.The vibration fatigue result of TC4 has shown that the stress level influences the life cycle a lot, higher the stress is, shorter the life would be, when the life is longer than 107 cycle, it is also possible to fail by crack; the vibration fatigue limit is 422 MPa, this number is similar with the vibration fatigue limit of TC4 blade.Fracture morphology of TC4 has shown that the material obeys brittle fracture under low-cycle, high-cycle and very high-cycle, the fracture is trans-granular and inter-granular, the number of cracks has a negative correlation with stress, the crack growth rate has a positive correlation with stress at rapid propagation area, the crack initiate in the direction of shear stress and tend to perpendicular with the stress, when it achieved, the crack growth rate has an obvious increase.Vibration fatigue result of welded joints have shown that the failure position under higher stress is fine-grained zone of the heat affect zone, the life is worse than the base metal with same amplitude; the failure position under lower stress is weld seam, the life is better than the base metal.Vibration fatigue fracture morphology has shown that the welded joints are brittle fracture; the crack growth rate is obviously higher than base metal, the period of crack initiation takes longer, the surface depression can grow into crack source, leading nearly 10 percent of decline of life; chain porosities haven't grow into sources, but they have influenced the crack growth rate and direction, leading nearly 20 percent of decline of life.