Solidification of Ni-Mn-Ga magnetic shape memory alloy built via laser powder bed fusion on a single crystal substrate

Abstract

Ni-Mn-Ga-based magnetic shape memory (MSM) alloys have significant potential as fast actuation materials due to their ability to undergo large magnetic-field-induced strains in an external applied magnetic field. This study explored the manufacture of Ni-Mn-Ga via the laser powder bed fusion (PBF-LB/M) additive manufacturing process, aiming to determine the parameter combinations that enhance the development of a crystallographically oriented coarse grain structure. In the first part of the study, the single tracks were melted on pre-heated single-crystalline Ni-Mn-Ga substrates by varying the applied laser power and scanning speed. This experiment revealed the existence of a parameter window where epitaxial solidification of the single-track can be achieved. Additionally, the results demonstrated that preheating prevents cracking of the single-crystal substrate. Subsequent experiments using a thin-walled 3D geometry demonstrated that this epitaxial structure was replicated across multiple layers, with the built samples exhibiting crystallographically oriented oligocrystalline structures following a high-temperature homogenization treatment. PBF-LB/M shows high potential for facilitating the additive manufacturing of oriented coarse grain oligocrystals for the production of microscale actuators.