Influence of laser powder bed fusion scanning strategies on microstructure, transformation, and magnetic behavior of Ni-Mn-Ga magnetic shape memory alloys
Meysam Norouzi-Inallu, Ville Laitinen, I. Orue, K. Ullakko
Abstract
Additive manufacturing via laser powder bed fusion (PBF-LB) offers new possibilities for producing complex Ni-Mn-Ga magnetic shape memory (MSM) actuators. However, the functional performance of these alloys remains limited by compositional deviations and microstructural constraints introduced during processing. This study investigates how PBF-LB parameters—specifically scanning speed and hatch distance (Batch 1), as well as scanning strategy, including unidirectional, bidirectional, and rotated scan vectors (Batch 2)—affect manganese evaporation, relative density, crystal structure, martensitic transformation behavior, and magnetic properties of Ni-Mn-Ga MSM alloys. A volumetric energy density (VED) of approximately 50 J/mm³ was found to produce a five-layered modulated tetragonal martensitic structure at ambient temperature, whereas at a higher VED of 65 J/mm³, the structure was seven-layered orthorhombic martensite. The unidirectional approach led to increased cracking and unstable processing, whereas rotating the scan vector in bidirectional scans had minimal impact on magnetic or structural properties. These findings contribute to a growing understanding of how PBF-LB processing parameters influence the functional performance of Ni-Mn-Ga alloys. • Volumetric energy density control phase formation, enabling the build 10 M, 14 M, and NM martensites in Ni-Mn-Ga MSM alloys via PBF-LB. • Bidirectional strategy enhances process stability, achieving higher relative densities and reduced defects, independent of scan vector rotation. • Magnetic and transformation behavior correlate with Mn content, emphasizing the need to minimize Mn loss during PBF-LB to optimize magneto-structural performance.