Filament extrusion-based additive manufacturing of NiTi shape memory alloys

Integrated additive manufacturing of actuators based on active materials could potentially replace conventional motors in numerous applications across disciplines like biomedical engineering, robotics, or aerospace. In this work, extrusion-based additive manufacturing of functional NiTi shape memory alloys is demonstrated via 3D printing of filaments consisting of thermoplastic binder and metal powder. Two alloys are fabricated, one showing superelastic, the other showing shape memory properties at room temperature. The microstructures of both alloys are characterized and set into perspective with the measured thermo-mechanical properties. The 3D-printed NiTi showed a shape memory strain of 1.9 %, respectively a superelastic strain of 1.3 % for an applied strain of 4 %. To enlarge the shape memory strain actuator geometries are designed, fabricated, and tested. The results of this study may find application in the field of additive manufacturing of active structures, also referred to as 4D printing. Commonly, polymeric materials are used in such structures, which often suffer from poor mechanical properties and durability. The use of metallic materials as it is investigated in this work could help to overcome these limitations.