Corrosion applications such as nuclear energy and prosthesis demand minimization of manufacturing defects commonly found in additive manufacturing. Porosity is correlated with pit initiation, propagation and SCC (stress corrosion cracking). Grain boundaries between phases are also susceptible to corrosion (1). Printing parameters such as power input, material feed rate, scan velocity, layer thickness and mesh size all affect microstructure in printed metal (3). Holding these constant, scan length is another parameter that can be studied. Scan length describes the distance traveled by the laser or electron beam before it reverses direction, to fuse an area adjacent to its immediate path, or “hatches.” Scan vector length has been found to decrease part density and increase cracking (2). This project investigates the effect of scan length on porosity and phase separation.

With greater scan length, porosity increased in the titanium samples. With greater percent completion in the build, porosity decreased. Void size was not necessarily correlated with these parameters, but void prevalence was. Increased density and uniformity as a build progresses is expected, because as more layers are sintered, the temperature gradient between the previous layer and current layer decreases and stabilizes. A similar phenomenon takes place in hatching, on the cross sectional level. As seen in the bar with short scan length, greater uniformity and lesser porosity is achieved when the temperature gradient between adjacent scan vectors is minimized. Long scan lengths increase this gradient and result in lack of fusion defects.