Additive manufacturing of NiTi shape memory alloys is challenging due to their sensitivity to composition and thermal history. The gap between high-resolution powder-based AM and high-productivity wire-based processes for NiTi remains a challenge. This study investigates the technical feasibility of depositing Ni-rich NiTi (56 wt.% Ni) using a micro gas metal arc-based directed energy deposition (µ-GMA-DED) process with a 300 µm wire. The investigation was conducted on a single-bead, single-layer geometry deposited onto a titanium substrate. The deposited layer exhibited a heterogeneous microstructure with dendritic and eutectic-like regions, where phase analysis revealed a mixture of NiTi and Ni3Ti intermetallics. Differential scanning calorimetry showed suppression of the martensitic transformation in the as-deposited condition, likely due to the high fraction of non-transformable Ni3Ti, compositional redistribution during rapid solidification, and potential substrate dilution. The nanoindentation results reflected this heterogeneity, with Young’s modulus ranging from 64 to 151 GPa. While post-deposition heat treatment partially restored the martensitic transformation, these results demonstrate the preliminary feasibility of the µ-GMA-DED process, noting that strict control over chemistry and dilution is required before the route can be applied to functional components.
Dornelas et al. (Fri,) studied this question.