Additive manufacturing of Ni-Mn-Sn shape memory Heusler alloy -- Microstructure and magnetic properties from powder to printed parts

TL;DR

This study explores the microstructure and magnetic properties of Ni-Mn-Sn Heusler alloys processed via additive manufacturing, highlighting the effects of processing conditions on phase transition temperatures and magnetic behavior.

Contribution

It provides new insights into how additive manufacturing affects the microstructure and magnetic properties of Ni-Mn-Sn alloys, emphasizing the importance of composition control.

Findings

Polycrystalline microstructure with elongated grains formed during processing.

Complete martensitic transformation achieved after heat treatment.

Mn evaporation and oxidation influence transition temperature and magnetization.

Abstract

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.