Effect of process parameters on non-modulated Ni-Mn-Ga alloy manufactured using powder bed fusion

Increasingly, metal parts made by additive manufacturing are produced using powder bed fusion (PBF). In this paper we report upon the combined effects of PBF parameters, including power and scan speed, in layer-by-layer manufacturing of gas atomized non-modulated (NM) Ni-Mn-Ga alloy. The effects of process parameters upon PBF is studied by applying nine different parameter sets in the as-printed state and after homogenization and ordering. The chemical composition of the samples is analyzed using EDX attached to an SEM, and the crystal structures are determined by X-ray diffraction. The phase transformation temperatures are measured using a low-field ac susceptibility measurement system and the magnetic properties are measured with a vibrating sample magnetometer (VSM). Before the heat-treatment, all as-printed samples showed paramagnetic behavior with low magnetization and no phase transformations could be observed in the susceptibility measurements. After annealing, the samples recovered the ferromagnetic behavior with comparable magnetization to annealed gas atomized powder. The as-printed samples were composed of a mixture of different crystal structures. However, after annealing the original NM structure with a = b = 5.47 Å and c = 6.66 Å with a c/a -ratio of 1.22 was recovered and crystallographic twins could be observed in an SEM.