  Ni-Mn-based Heusler alloys like Ni-Mn-Sn show an elastocaloric as well as
magnetocaloric effect during the magneto-structural phase transition, making
this material interesting for solid-state cooling application. Material
processing by additive manufacturing can overcome difficulties related to
machinability of the alloys, caused by their intrinsic brittleness. Since the
magnetic properties and transition temperature are highly sensitive to the
chemical composition, it is essential to understand and monitoring these
properties over the entire processing chain. In the present work the
microstructural and magnetic properties from gas-atomized powder to
post-processed Ni-Mn-Sn alloy are investigated. Direct energy deposition was
used for processing, promoting the evolution of a polycrystalline
microstructure being characterized by elongated grains along the building
direction. A complete and sharp martensitic transformation can be achieved
after applying a subsequent heat treatment at 1173 K for 24 h. The
Mn-evaporation of 1.3 at. % and the formation of Mn-oxide during DED-processing
lead to an increase of the transition temperature of 45 K and a decrease of
magnetization, clearly pointing at the necessity of controlling the
composition, oxygen partial pressure and magnetic properties over the entire
processing chain.
