Dealloying significantly improves the fatigue property of laser-welded joints of TC4 titanium alloy

Titanium (Ti) alloys, characterized by the high specific strength, corrosion resistance, and non-magnetic nature, have been widely applied to the manufacturing of nuclear submarines, deep-diving submersibles, and aerospace equipment. Therein, TC4 is the most widely applied Ti alloy nowadays. The effects of incorporating pure Ti into the weld on the fatigue behaviors of laser-welded joints made from TC4 Ti alloy were studied. Experimental results demonstrate that the incorporation of titanium in the weld of butt joints enhances fatigue strength by 15%. The reduction in the microhardness gradient of joints is a significant factor contributing to the enhanced fatigue performance of laser-welded joints. The microhardness of the weld zone of TC4 laser welded joint was significantly reduced after Ti was added. Changes in the proportions of alloying elements and microstructures in the weld are important causes for the reduction of microhardness. Compared with the joints without addition of Ti, adding Ti can enlarge the size of acicular α′ martensite in the WM.