Fused Filament Fabrication of NiTi Components and Hybridization with Laser Powder Bed Fusion for Filigree Structures

Johannes Abel; Anne Mannschatz; Robert Teuber; Bernhard Müller; Omar Al Noaimy; Sebastian Riecker; Juliane Thielsch; Björn Matthey; Thomas Weißgärber

doi:10.3390/ma14164399

Fused Filament Fabrication of NiTi Components and Hybridization with Laser Powder Bed Fusion for Filigree Structures

Materials (Basel). 2021 Aug 6;14(16):4399. doi: 10.3390/ma14164399.

Authors

Johannes Abel¹, Anne Mannschatz¹, Robert Teuber², Bernhard Müller³, Omar Al Noaimy³, Sebastian Riecker², Juliane Thielsch³, Björn Matthey¹, Thomas Weißgärber²

Affiliations

¹ Fraunhofer Institute for Ceramic Technologies and Systems (IKTS), Winterbergstraße 28, 01277 Dresden, Germany.
² Fraunhofer Institute for Manufacturing Technology and Advanced Materials (IFAM), Winterbergstraße 28, 01277 Dresden, Germany.
³ Fraunhofer Institute for Machine Tools and Forming Technology (IWU), Nöthnitzer Str. 44, 01187 Dresden, Germany.

Abstract

The present study introduces an approach to the powder metallurgical shaping of a pseudo-elastic nickel-titanium (NiTi 44 alloy) combining two different Additive Manufacturing (AM) processes, namely fused filament fabrication (FFF) and Laser Powder Bed Fusion (LPBF), by manufacturing filigree structures on top of sintered FFF parts. Both processes start with commercial gas atomized NiTi powder, which is fractionated into two classes. Using the fine fraction with particle sizes <15 µm, robust thermoplastic filaments based on a non-commercial binder system were produced and processed to different auxetic and non-auxetic geometries employing a commercial standard printer. FTIR analysis for thermal decomposition products was used to develop a debinding regime. After sintering, the phase transformation austenite/martensite was characterized by DSC in as sintered and annealed state. Precipitates resulting from residual impurities were detected by micrographs and XRD. They led to an increased transformation temperature. Adjusting the oxygen and carbon content in the alloy remains a challenging issue for powder metallurgical processed NiTi alloys. Filigree lattice structures were built onto the surfaces of the sintered FFF parts by LPBF using the coarser powder fraction (15-45 µm). A good material bond was formed, resulting in the first known NiTi hybrid, which introduces new production and design options for future applications.

Keywords: Additive Manufacturing (AM); Laser Powder Bed Fusion (LPBF); Shape Memory Alloy; fused filament fabrication (FFF); hybridization; nickel–titanium; nitinol; pseudoelastic alloy; smart material; superelastic alloy.