Microstructural Evolution and Functional Performance of Ni-Ti-Hf SMA Structures produced via powder bed based Additive Manufacturing Techniques

Shape memory alloys (SMA), such as Ni-Ti, gained a lot of attention as promising candidates, especially for actuation applications. While Ni-Ti SMA are typically limited to application temperature windows below 100 °C, additions of Hf can increase the transformation temperatures and, thus, the temperature range for application. However, significant additions of Hf result in an increase of brittleness, limiting the thermomechanical processing window for manufacturing springs, tubes and others. Additive manufacturing (AM) processes may help to overcome this issue, since these processes allow for manufacturing of near-net shaped functional materials in various geometries. The present study focuses on a Ni-Ti-Hf SMA processed via powder bed fusion processes, i.e. E-PBF and L-PBF. The impact of process induced defects and the microstructural evolution on the functional properties is discussed. Furthermore, the feasibility of manufacturing different complex geometries is presented.