Slender structure of nickel-titanium shape memory alloy fabricated by continuous directed energy deposition

The continuous directed energy deposition (DED) method has been utilized to process various kinds of slender structures with different materials due to its uninterrupted characteristics. The characteristics of the specimen fabricated by this continuous DED method may not be the same as that in the conventional DED method due to different temperature histories. In this study, the characteristics of NiTi shape memory alloy on phase constituent and microstructure are investigated. Results indicate that the specimen fabricated with higher laser power shows more Ti2Ni precipitation, increased defects (e.g., voids, inclusion, etc.), and larger grain size. The microstructure at different regions presents diverse morphologies, which change from columnar dendrite to equiaxed grain to columnar dendrite due to different cooling rates. The preliminary study in this paper is expected to lay the foundation for the fabrication of NiTi slender structures with the continuous DED method.