Altered phase transformation behaviors and enhanced bending shape memory property of NiTi shape memory alloy via selective laser melting

Selective laser melting (SLM) of NiTi shape memory alloys (SMAs) was studied systematically for the resulting density and surface roughness. It was found that high laser energy density could not guarantee dense SLM NiTi SMAs. Furthermore, the phase composition and transformation temperatures varied remarkably with delicate change of laser power and scanning speed. Mechanical tests suggested that the SLM NiTi alloys made under the optimal process parameters (70 W in laser power and 105 mm/s in laser scanning speed) had an ultimate tensile strength of 788 MPa, an elongation of 7.43% in austenite state. Bending shape memory test revealed that 100% recovery rate was obtained in a sequent bending test (45°→90°→180°→270°→360°), and the bending deformation was fully recovered in ten-time cycle bending test at 180°, and recovery rate was 97% after ten-time cycle bending test at 360°. The excellent bending shape memory properties was attributed to high-density dislocations and Ti2Ni nanoprecipitates which impeded the occurrence of plastic deformation effectively. The findings in this study demonstrated that SLM NiTi parts had excellent shape memory properties and was promising for industrial applications.