LPBF process windows mapping for shape memory and superelastic NiTi alloys: A comparative study

Additive manufacturing (AM) forges the pathway of nickel-titanium (NiTi) based technology valorization as an effective manufacturing solution for the otherwise difficult-to-process material. Creating a hierarchical structure of Ni-Ti is currently a quite explored domain in AM technology, in which the laser powder bed fusion (LPBF) process is a preferred method to fabricate the intricate structure due to its ability to maintain a high-resolution accuracy. NiTi alloys exhibit two notable smart properties: superelasticity and shape memory effect. Depending on the Ni content, the pre-alloyed powders for the LPBF process inherently favor one of these functionalities. Ni-43.15Ti wt.% typically demonstrates superelastic behavior at room temperature, while those with a composition of Ni-44.15 wt.% tend to exhibit shape memory effects. The printing process, on the other hand, might also cause the selective evaporation of Ni, which may directly impact the transformation temperature and consequently affect the functional behavior of the printed parts. Therefore, a comparative study of these two commercially available powders that focuses on print quality, the degree of Ni loss, and the subsequent transformation temperature is essential for understanding and controlling performance outcomes. A design of experiment (DOE) which explores the overall print quality on various applied laser power (P) and scanning velocity (v) is conducted. The resulting prints are then characterized to assess their subsequent overall structural integrity using X-ray computed tomography (XCT), transformation temperatures using differential scanning calorimetry (DSC), and Ni content using energy-dispersive spectroscopy (EDS). This study highlights how the printing parameters affect the overall quality and functional performance of the printed NiTi alloy.