Low cycle fatigue properties and fracture behavior of electron beam welded joints of TC4 titanium alloy

Low-cycle fatigue performance between 30 mm thick TC4 electron beam welded joint and base material was compared in the paper.The experimental results showed that the low-cycle fatigue performance of base material was slightly better than that of welded joint,and the strain fatigue limits of base material and welded joint were 0.49% and 0.44%,respectively.The fatigue fracture location of welded joint was observed,and the fatigue fracture location of welded joint was in the weld.The fatigue fracture morphology of base material and welded joint was observed,and the fatigue crack source appeared on the surface of the sample.Typical fatigue lines were found in the fatigue crack propagation area,but spacing between fatigue lines of welded joints was smaller than that of base material.Dimples were found in the fracture zone,which belonged to ductile fractures.Finally,a high-resolution SEM was used to study the microstructure of welded joint.Base material appeared a typical two-state microstructure,which was mainly composed of equiaxed α phase and intracrystalline β.The edge of the equiaxed α phase in the heat-affected zone gradually dissolved and transformed into lamellar α’phases.Weld was mainly composed of basket-like microstructure that was made up of needle-like α’phases.Highlights:(1)The reason why the overall low cycle fatigue performance of the electron beam welded joint of 30 mm TC4 titanium alloy was weaker than that of the base metal and fracture in the weld zone was clarified.The microstructure of the joint was highly uneven and the microhardness of the weld zone was lower than that of the heat affected zone on both sides.(2)It was revealed the reason that the microhardness of the weld zone of 30 mm TC4 titanium alloy electron beam welding was lower than that of the heat affected zone,and there were more martensite α’phase in the heat affected zone near the weld side.(3)By observing the fatigue fracture of the base metal and joint,it was found that fatigue glint appeared in the fatigue crack propagation area of the base metal,while fatigue striation spacing of the weld zone was smaller than that of the base metal.