EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Wire-based electron beam additive manufacturing (AM) has become an efficient and attractive directed energy deposition technique to produce mid-size near-net-shape parts. Due to the electron beam, the manufacturing takes place in a vacuum chamber, thus protecting the material from deleterious impurity pick-up. Important structural materials, such as titanium and aluminum, do not reflect the beam due to its concentrated high energy. Hence, when compared to laser-based techniques, electron beam presents higher energy efficiencies. Moreover, energy losses decrease to near zero when using wire as a feedstock. Therefore, wire-based electron beam AM (or electron beam freeform fabrication – EBF3) has gained momentum. AM has been playing an important role in broadening the deployment of materials of difficult processability. As an example, one can highlight NiTi shape memory alloys, a unique alloy regarding its functional property: strain recovery after stress releasing (superelasticity) or heating (shape memory effect). Powder bed fusion techniques - such as selective laser melting - have been applied for this alloy. Nonetheless, the processing of NiTi by wire-based techniques was barely explored, and thus a new field of investigations has emerged. Based on this fact, this work aims to evaluate the effects of the process parameters on the structural integrity, microstructure, and mechanical behavior of NiTi additively manufactured by EBF3. This investigation used the Box-Behnken DoE to correlate process parameters and material properties of EBF3 specimens. Statistical analysis was used to understand how beam current, welding, and feeding speed influenced the fabrication process. EBF3 specimens’ microstructure was characterized by optical and scanning electron microscopy, and thermophysical analysis. The mechanical assessment of produced and heat-treated parts was performed in compression mode, taking into consideration the strain recovery of the superelastic behavior. Thus, a relationship between process parameters, microstructure, and mechanical performance was established.