4D printing of net shape parts made from Ni-Mn-Ga magnetic shape-memory alloys

This work 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 both relatively easy control of part porosity and the possibility to obtain complex shaped parts from Ni-Mn-Ga alloys. The four-dimension (4D) is created by the predictable change in 3D printed part configuration over time as the result of shape-memory functionality. 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 good mechanical strength. Parts with porosities between 24.08% and 73.43% have been obtained by using powders with distinct morphologies. The printed Ni-Mn-Ga parts undergo reversible martensitic transformation during heating and cooling, which is a prerequisite for the shape-memory behavior. Thermo-magneto-mechanical trained 3D printed parts obtained from ball milled Ni-Mn-Ga powders showed reversible magnetic-field-induced strains (MFISs) of up to 0.01%. The additive manufacturing is a viable technology in solving the design issues of functional parts made of Ni-Mn-Ga magnetic shape-memory alloys (MSMA).