Designing Titanium Alloys for Additive Manufacturing

In general, the additive manufacturing (AM) of components involving titanium alloys has been restricted to known alloys, e.g., Ti-64. Unfortunately, there are at least three problems associated with such manufacturing of these alloys, involving the presence of coarse columnar microstructures, porosity, and the presence of significant residual stresses. Solutions to the first two of these may be addressed by alloying schemes, whereas the third probably requires a process modification. The present research, described in this presentation, has been aimed at developing new alloys for which these problems have been solved, i.e., alloys designed deliberately for the manufacturing process, in this case AM. Regarding the coarse columnar structures, alloying additions that cause a change in solidification mode have been developed, which include alloying additions of Fe, Ni and Cu. Critical concentrations of these alloying elements have been determined such that transitions from columnar to equiaxed morphologies are produced. The porosity present in the builds has been characterized by X-ray µ-CT measurements and serial sectioning, followed by image reconstruction. It has been shown that there are two different scales of defects present, and these will be discussed in the presentation. This research has been sponsored by AFRL/RX.