Laser powder bed fusion of (14 M) Ni-Mn-Ga magnetic shape memory alloy lattices

Abstract

Recent developments in the additive manufacturing of magnetic shape memory (MSM) alloys have demonstrated the high potential of laser powder bed fusion (L-PBF) process for the manufacture of functional polycrystalline Ni-Mn-Ga-based actuating devices with complex geometries. This research utilises a systematic experimental approach to develop and optimise an L-PBF process for manufacturing Ni-Mn-Ga lattices. Experiments were conducted in two distinctive stages: firstly, to characterise the selective Mn evaporation in bulk samples built; secondly, to investigate the influence of the applied process parameters on the relative density and geometrical integrity of the lattice struts. The lattices manufactured using optimised parameters had a high internal density of ~99% and were heat-treated for chemical homogenisation, grain growth, and atomic ordering. The heat-treated lattices exhibited a seven-layered modulated (14 M) martensite structure at ambient temperature with the phase transformation temperatures and magnetic properties corresponding to the chemical composition. Primarily, the results demonstrate that the beneficial ‘bamboo-grained’ structure can be obtained in individual lattice struts via post-process heat treatment. Plus, they also confirm that the use of thinned-down structures, such as lattices, can effectively prevent the cracking previously observed in bulk samples. Although there remains plenty of room for further research on this topic, these results highlight the high potential of L-PBF for the manufacture of a new generation of MSM-based actuating devices.