Physical Simulation of microstructures generated by wire-arc directed energy deposition

Titanium alloys are widely used in modern aviation due to their high strength-to-weight ratio, enabling the production of highly loaded and lightweight components. Manufacturing of titanium parts by machining out of solid pre-materials produces much waste material. Wire-arc directed energy deposition (waDED) conversely processes this energy-intensive material highly efficient, however requiring it in wire form for deposition using a welding power source. This process provides a characteristic thermal profile with high cooling rates and cyclic reheating/cooling during buildup, so that established titanium alloys develop large columnar grains in buildup direction, causing anisotropic mechanical properties. The efforts on the process side can hardly resolve the unfavourable characteristic microstructures. Therefore, research focuses on material-based solutions using the interdependence theory, which however entails that testing novel titanium alloy compositions requires wire manufacturing, to assess the microstructure emerging upon additive manufacturing (AM). Physically simulating potential AM microstructures, omitting the wire drawing step of experimental alloys, would accelerate alloy screening. Hence, EBM and Plasma or GTAW are used to fabricate single weld beads without filler wire on wrought and AM titanium substrates. Resulting microstructures compared with unmodified substrate material show the advantages of each technique aiming at the identification of the most relevant. Temperature recordings during weld bead fabrication and reference layer deposition reviews the thermal histories. Characterization is performed using scanning electron microscopy, light microscopy, microhardness measurements and bending tests. This comparison evaluates whether an alternative approach without wire manufacturing and deposition, can create similar microstructures, facilitating the screening of titanium alloys for AM.