Electrically Actuated Shape Recovery of NiTi Components Processed by Laser Powder Bed Fusion after Regulating the Dimensional Accuracy and Phase Transformation Behavior

Abstract

To develop self-recovery intelligent components based on resistance heating and obtain satisfactory performance in practical applications, this study optimized the forming quality, dimensional accuracy, and phase transformation temperatures of Nickel-titanium (NiTi) alloys by controlling the process parameters. The tensile properties and shape-memory effects of the NiTi alloys prepared using the optimized process were clarified. The relationship between the change in temperature and the shape recovery process of the deformed structure under electrical excitation was investigated. The results show that the suitable processing window for ensuring the forming quality without noticeable distortion and macro cracks depends on the laser parameters. In both the X and Y directions, the measured dimensions increased with an increase in laser power and first decreased and then stabilized with an increase in scanning speed. The XRD results showed that all the as-built samples consisted of B2 austenite and B19’ martensite phases and Ni₃Ti. Mechanical tests suggested that excellent tensile properties with a tensile strength of 753.28 MPa and elongation of 6.81% could be obtained under the optimal parameters of 250 W and 1200 mm/s. An excellent shape-recovery rate of 88.23% was achieved under the optimal parameters. Subsequently, chiral lattice structures were successfully fabricated by laser powder bed fusion (LPBF) under the optimal parameters, and a shape-recovery rate of 96.7% was achieved under electrical actuation for a structure with a pre-compressed strain of 20%. This study also found that the temperatures at the grasp regions were always higher than those at other positions because of the generation of contact resistance at the grasp regions. This facilitates the rapid recovery of the structure at the grasp regions, which has important implications for the design iteration of NiTi smart components.