Improved recoverable strain and wettability by beam offset in LPBFed porous NiTi scaffolds

We report a strategy to balance manufacturing accuracy with the resultant wettability and recoverable strain of porous Ni-rich Ni 51.2 Ti 48.8 shape memory alloy (SMA) scaffolds, by regulating beam offsets (0, 20, and 40 μm) during laser powder bed fusion (LPBF) processing. Results show that with the increased beam offsets, the porosity deviation from the designed value (70.11%), denoting manufacturing accuracy of the porous SMA scaffolds, decreases from 14.33% to 7.8% and 3.1%, accompanied by nearly full density of scaffolds struts. Concurrently, grain size, low-angle grain boundaries (LAGBs), KAM values, and dislocation density are progressively reduced; the compressive fracture strength decreases from 271.2 MPa to 177.2 MPa and 106.4 MPa; the elastic modulus reduces from 10.4 GPa to 6.61 GPa and 3.51 GPa; the water contact angle indicating wettability first diminishes from 103.9° to 29° and then rises to 57.1°. Given the excellent wettability of the porous SMA scaffolds with a 20 μm beam offset, a typical functional property in some special application fields, corresponding recoverable strain was evaluated to be 9.3%, exceeding those of various porous NiTi scaffolds fabricated by additive manufacturing. The favorable combination of high wettability and large recoverable strain is primarily attributed to the moderate pore size resulting from appropriate manufacturing accuracy, as well as the intact strut architecture and low dislocation density within columnar grains. These findings may facilitate the development of high-performance porous NiTi scaffolds for diverse engineering and biomedical applications.