Abstract: For TC18 titanium alloy formed by electron beam rapid manufacturing, the microstructure characteristics, fracture behavior and fracture causes of the TC18 titanium alloy were studied by means of optical microscope(OM), scanning electron microscope(SEM) and energy spectrum analysis(EDS). The results show that the tensile fracture mode of the TC18 titanium alloy is a mixture of both positive fracture and cut-off fracture. The fracture mechanism is intergranular ductile fracture and transgranular dimple-fracture, which originate from the grain boundaries. After hot isostatic pressing, a large amount of Widmannstatten structure is produced, which is one of the important factors leading to the decrease of the plasticity. The grain boundary structure can be improved by high temperature treatment and the tensile plasticity along forming direction can be increased to more than 7% under the condition of little change in strength. Because the grain of the TC18 titanium alloy formed by electron beam fuse is abnormally coarse and grain size is not uniform, the thin-wall structure performance is greatly affected by a single grain.

Key words: electron beam rapid manufacturing, microstructure, TC18 titanium alloy, fracture mechanism, plasticity