Fig. 1. (a) The stripe rotation scanning strategy with stripe width of 4 mm and hatch rotation θ = 67°. The laser goes through “Black Regions” (black arrows) first and then “White Regions” (red arrows) in each layer. (b) The SLM-produced lath-shaped NiTi samples built on NiTi substrate. (c) DSC graph of the SLM-NiTi. (d) XRD pattern of the SLM-NiTi after cooled in liquid nitrogen.

Fig. 2. Tensile deformation behavior of the SLM-NiTi. (a) Tensile stress-strain curve at RT. (b) Comparison of tensile fracture strength and fracture strain between our work and reported SLM-produced NiTi [10,20,21].

Fig. 3. (a)-(c) SEM secondary electron micrographs of the SLM-NiTi from top view, side view and front view, respectively. The inserts are the micro-defects in magnified view.

Fig. 4. (a) Etched optical micrographs of the SLM-NiTi in side view. (b) Schematic diagram of microstructures in the partial area. The yellow dotted line represents the molten pool boundary; red dotted lines represent the radial grain boundary in a molten pool; the blue line represents the flexural zigzag grain boundary throughout multilayers. (c) Etched optical micrographs of the cracks upon tension.

Fig. 5. (a) Stress-Strain-Temperature curves obtained by tensile loading-unloading-heating process of the SLM-NiTi. (b) Shape recovery rate as a function of tensile pre-deformation. (c) The initial shape of printed SLM-NiTi part. (d) The compressed SLM-NiTi part with deformation of 50%. (e) The recovered shape of the SLM-NiTi part after heating.