Epitaxial re-solidification of laser-melted Ni-Mn-Ga single crystal

Additive manufacturing (AM) of magnetic shape-memory alloys (MSMAs) allows fuller use of geometry in the design of MSMA parts and avoids the segregation and high cost associated with single crystal production. While most research effort in AM of MSMAs pursues functional foams or polycrystals, epitaxial growth during liquid-phase AM may enable fully-dense single-crystalline MSMA parts, with associated availability of the full blocking stress. We melted a Ni₅₁Mn_24.4Ga_24.6 single crystal with a moving laser spot under several process parameter combinations of laser power and velocity. While tracks created with lower laser travel velocity were almost entirely epitaxial, the track created with highest velocity (10 mm/s) included non-epitaxial columnar grains and grains at the top of the track. Synchrotron-based high-energy diffraction microscopy (HEDM) experiments revealed that mosaic spread of epitaxial material was slightly higher than that of surrounding non-re-solidified material. Our results demonstrate epitaxial growth of Ni-Mn-Ga with minimal grain content using full-melting laser processing.