Study On The Micro-vibration Fatigue Factors Of TC4 And Welded Joints Of Micro-plasma Welding

The foreign objects flowing with the high-speed air could cause damage to engine blade during taking off, landing and low-altitude flight of aircraft, which is called foreign object damage(FOD) and accounts for over 40% of engine maintenance. In this paper, TC4 titanium alloy and micro-plasma arc bead welding connector subjected to FOD were investigated by means of low-speed impact model with drop hammer. The microstructure and fatigue life of TC4 and welding connector after FOD were analyzed with micro-vibration fatigue test, and the influence of porosity in weld defect on the fatigue life of welding connector was also researched.The damage zone of sample after drop hammer test was featured by tiny cracks, micro-structure damage and heat-insulation cutting belt, which was typical micro morphology of FOD. TC4 and welding connector after FOD were consisted of surface serious deformation, sub-surface plastic deformation and heat-insulation cutting belt. As the impact energy reached to 4 J, amount of micro cracks appeared on the TC4 titanium alloy surface. As the energy increased to 6 J, heat-insulation cutting belt and tiny holes were found on the titanium alloy because of plastic deformation, and the holes increased without cracks as the energy was 8 J. Besides, welding connector impacted with energy of 4 J generated many micro cracks on the surface and tiny holes and heat-insulation cutting belt on the sub-surface, and the size of cracks increased with the impact energy.Micro-vibration fatigue test revealed that FOD could shorten the fatigue life of TC4 and welding connector, and the micro holes had no obvious effect on the the origination and propagation of fatigue crack. The micro cracks and heat-insulation cutting belt could become the fatigue crack initiation under the alternative load.After the micro-vibration fatigue test with porous welding connector, it was indicated that the welding pores could seriously shorten the fatigue life of components, and the pores could be the fatigue crack initiation. Additionally, the fatigue crack mechanism caused by the pores was crispy breakage.