Revealing effects of powder reuse for LPBF-fabricated NiTi shape memory alloys

Abstract

In metal-based additive manufacturing processes, such as laser powder bed fusion (LPBF), the powder utilization is often less than 50%. Considering the cost efficiency, powder reuse is needed for an economical and sustainable LPBF process. As intermetallic compounds, LPBF-fabricated NiTi alloys are characterized with phase transformation behaviors, mechanical properties and functions that are very sensitive to possible changes in powder characteristics caused through reuse, but the exact effects are still poorly understood. Here, the LPBF process has been repeated ten times using the virgin powder supplement method. Results show that the oxygen content of NiTi powders rises from 370 to 752.3 ppm with the enhancement of the reuse cycle number. Powder oxidation enhances the laser absorptivity of the powder bed, leading to an increase in surface roughness and porosity of NiTi parts. Compared to the specimens made from virgin powders, the mechanical property and shape memory function of specimens made from reused powders are degraded, mainly attributed to the oxygen impurity and deteriorated forming quality. This study allows making better decisions with regard to powder reuse in the development of performance-critical NiTi parts fabricated through LPBF.