Shape Memory Alloys

NiTi is a versatile material with inherent properties such as biocompatibility, shape recovery and superelasticity. However, the application of NiTi components in engineering systems is limited by the availability of suitable geometries. Most commercial off-the-shelf geometries are simple and limited in freedom of shape such as wires, rods, and springs. With powder bed fusion for metals (PBF-LB/M) a manufacturing technique is present of producing complex shaped and highly customized geometries. The capabilities of PBF-LB/M combined with the unique properties of NiTi can lead to novel developments in fields of biomedical, aerospace or robotics.

Fig. 1: one-way shape memory effect (OWSME)

The research conducted aims to understand the impact of processing NiTi with PBF-LB/M on functional and mechanical properties over a wide range of processing parameters in comparison to conventional manufactured NiTi. The feedstock powder is crucial and affects the properties of the processed parts. However, the powder behaves significantly different compared to the same composition of conventional bulk NiTi. In addition, Ni evaporation through process parameter variation, such as laser power and scanning speed, is the governing factor when it comes to mechanical and functional characterization. In turn, the evaporation of Ni gives unique possibilities to tailor the functional properties, in particular the transformation behavior responsible for the shape recovery, to manufacture thermal graded monolithic and complex formed structures, which is not possible with conventional manufacturing. This is particular interesting for actuator applications, because with the developed technique sequential spatial actuation can be realized.

Fig. 2: two-way shape memory effect (TWSME)

Besides, we extensively study the two-way shape memory effect (TWSME) and its usage in potential novel applications. In contrast to the one-way shape memory effect (OWSME) the recovery strain can be obtained both during heating and cooling offering lightweight actuation for aerospace or micromechanism applications.