Mechanical ball-milling as a powder pretreatment for additive manufacturing of Ni-Ti shape memory alloy

Abstract A key challenge in additive manufacturing (AM) of metallic alloys is the absence of concurrent deformation processes during fabrication, which are crucial for optimizing microstructure and achieving properties comparable to those of wrought or thermomechanically processed materials. In this study, an approach to enhance the thermomechanical behavior of printed metals by mechanically preconditioning the feedstock powder is presented. Specifically, high-energy ball milling (HEBM) is applied to a Ni-Ti shape memory alloy (SMA) spherical powder prior to processing via the solid-state MoldJet AM technique. Our results show that HEBM lowers the sintering temperature and increases the sintered density, all while preserving the alloy’s thermal and superelastic mechanical properties. At the same time, the highly deformed morphology of the ball-milled powder is not evident in the sintered samples, which was attributed to the grain boundary migration and grain growth during sintering. These findings demonstrate the potential of HEBM as a beneficial pretreatment not only for SMAs but also for a broader class of metals processed through sinter-based AM, paving the way for further research into powder conditioning strategies in additive manufacturing.