Abstract: The balance elbow of ZTC10 titanium alloy in a vehicle fractured during service. Macro observation on fracture surface was carried out. The fracture is flat, with dim color; there are many small steps and lots of oval grains and dendritic structure on fracture. The propagation region presented fatigue characteristics, meaning the failure mode is fatigue fracture. The fracture was further analyzed with an optical microscope, a vickers hardness tester and a gas analyzer. It is shown that the fracture was typical welding structure; there were many air holes; around the holes, the micro-hardness was obviously higher and O content was also slightly higher than that of the normal zone. The stress state of the balance elbow, graphite production, casting and hot isostatic pressing process were analyzed. It can be concluded that due to the improper repair welding process control, there were a number of pores at the welding area, which was the main cause of the fracture of the ZTC10 titanium alloy castings.