4 Dimensional Printing And Characterization Of Net Shaped Porous Parts Made From Magnetic Ni Mn Ga Shape Memory Alloy Powders

Ferromagnetic shape memory alloys (FSMA's) are known to produce large strains in the presence of magnetic fields. Amongst the FSMA's near stoichiometric Ni2MnGa alloys present copious conceivable applications such as actuators and sensors due to these large magnetic field induced strains (MFIS's). Albeit, the large MFIS's are often observed in single crystals; which are difficult to manufacture and possess limited ductility. Recent investigations of polycrystalline Ni-Mn-Ga foams are reported to exhibit comparable MFIS's to those reported for single crystals. Therefore the ability to increase the MFIS in Ni-Mn-Ga alloys is envisioned through the introduction of pores in the microstructure. However, the manufacturing is difficult for all the above-mentioned Ni-Mn-Ga materials. Moreover, current techniques lack the ability to manufacture complex geometries. Additive Manufacturing (AM) via binder jetting is a method for producing porous near net shaped components utilizing micrometer sized material. This research investigates an additive manufacturing route of producing functional net shaped parts from pre-alloyed magnetic shape memory Ni-Mn-Ga powders. Three types of Ni-Mn-Ga powders were used in this investigation: spark eroded in liquid nitrogen (LN2), spark eroded in liquid argon (LAr), and ball milled (BM). Additive manufacturing via powder bed binder jetting, also known as 3D printing (3DP) was used in this research due to the ability to control part porosity and the possibility to obtain complex shaped parts from Ni-Mn-Ga alloys. The fourth-dimension (4D) is created by the predictable change in 3D printed part configuration over time as the result of shape-memory functionality. Powder characterization techniques including packing density measurements, size distribution analysis, and binder saturation experiments were conducted on the powders to obtain optimized printing parameters, respectively. The optimum layer thickness and binder saturation range was determined as 80 - 110 μm, and 110 - 250 %, respectively. Binder jetting of Ni-Mn-Ga powders followed by curing and sintering proved successful in producing net shaped porous structures (spring-like, 3-D hierarchical lattice structures, etc.) with suitable mechanical strength. Parts with porosities between 24.08 % and 73.43 % (1.164 g/cm3 to 6.35 g/cm3) have been obtained by using powders with distinct morphologies. The printed and sintered Ni-Mn-Ga parts undergo reversible martensitic transformations during heating and cooling, which is a prerequisite for the shape memory effect. Thermo-magneto-mechanical trained 3D printed parts obtained from ball milled Ni-Mn-Ga powders showed reversible magnetic-field-induced strains (MFIS's) of up to 0.01%. Binder jetting additive manufacturing is a viable technology in solving the design issues of functional parts made of Ni-Mn-Ga magnetic shape-memory alloys (MSMA).