4-D Printing of NiTi Shape Memory Alloys

Nickel-Titanium (NiTi) shape memory alloys (SMA) have been broadly employed to biomedical and aerospace industry due to its functional properties, namely shape memory effect (SME) and superelasticity (SE). Usually, NiTi is thermo-mechanically processed from cast ingots, thereafter forming into rods, bars, sheets and wires. For this purpose, the material must follow a complex combination of working conditions. However, intrinsic problems such as high reactivity and strength configure an additional challenge to their processing. Nonetheless, in the last decade additive manufacturing (AM) has shown be capable of overcoming such difficulties, once it enables the manufacturing of complex SMA parts of maintaining its desired functional properties [1].
In AM, powder-based processes have skyrocketed and, according to recent reviews, selective laser melting (SLM) is the main technique used for the processing of SMA. On the other hand, SLM and related powder-based processes still present two critical limitations: impurity pick-up (C, O and N) and part size limitation. One alternative to mitigate the aforementioned problems is found on the electron beam freeform fabrication (EBF3) technique. EBF3 uses electron beam as energy source and wires as feedstock, additively fabricating medium-to-large near net shape parts. In addition, since processing takes place in a vacuum chamber, the level of contamination is reduced. In reason of its versatility, this cutting-edge technology has gained importance achieving increasingly more acceptance for industrial applications. To the best of authors’ knowledge, there are currently no scientific work addressing the EBF3 fabrication of SMA. The present work addresses the first results on EBF3 of SMAs by studying NiTi alloys.