Microstructural evolution and magnetic properties of binder jet additive manufactured Ni-Mn-Ga magnetic shape memory alloy foam

This study investigated microstructural evolution, phase transformation and magnetic behavior of additively manufactured magnetic shape memory alloy foam. Pre-alloyed angular Ni-Mn-Ga ball-milled powder was binder jet printed and sintered at 1020 degrees C for 4 h in both vacuum and argon atmospheres. Porosity of the manufactured foams was studied using micro-computed x-ray tomography and it was found that the relative density of the sintered parts was about 50-60%. In the printed sample that was sintered in argon, electron microscopy with elemental analysis showed no compositional gradient. X-ray diffraction indicated that IOM modulated martensite was present in the pre-alloyed powder as well as the sample sintered in argon. Differential scanning calorimetry and thermomagnetic results showed that martensitic transformation of the sample sintered in argon was at 34 degrees C, while barely detectable in the sample sintered in vacuum. Saturation magnetization of the printed sample sintered in argon atmosphere was around 68.4 Am-2/kg. Production of a magnetic shape memory alloy by printing would enable complex-shaped elements for demanding applications, and intentionally including porosity could allow these polycrystals to exhibit the magnetic shape memory effect. Therefore, a facile method for sintering of Ni Mn Ga printed parts has been presented for the first time. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.