Manufacturing of Complex NiTi Geometries with LPBF and Adapted Scanning Strategies

Abstract NiTi shows a very promising combination of properties among different shape memory alloys. However, machining NiTi is a challenging task, making the manufacturing of complex geometries hard to nearly impossible using conventional manufacturing routes. As a result, the material’s full potential of the material has not been harnessed. The pseudoelastic properties of bulk NiTi are restricted to an 8 % strain. Additive manufacturing of NiTi using laser powder bed fusion (LPBF) has been demonstrated as a successful alternative production route, capable of exhibiting pseudoelastic behavior even in the as-built state. Existing literature has shown that modifications of the processing parameters can change the properties of Ni-rich NiTi significantly, which can be utilized intentionally to control the pseudoelastic properties in LPBF-manufactured NiTi. The fabrication of porous and lattice structures using LPBF allows to attain specific properties. This is achieved not only through the adjustment of the laser parameters and scanning pattern but also by enabling the creation of specifically tailored feature sizes and geometrical designs, such as unit cell design, the number and distribution of unit cells, and gradation. These geometrical structures go beyond the conventional unit cell designs (like the bcc unit cell), and when combined with the unique material behavior, they can result in extraordinary properties. It is possible to create a programmable material whose behavior can follow a logical description. The influence of lattice structure geometry and manufacturing parameters on the mechanical and functional performance will be discussed in the following. In addition, we present a structure whose stiffness behavior follows an if-then-else statement regarding to the effective strain and permits an effective strain exceeding 20 % without failure. The structure can be implemented in a planar clamping element which allows an adjustment to different shapes because of the high and low stiffness in different strain ranges.