Tailoring the microstructure, martensitic transformation temperature and mechanical properties of 4D printed NiTi alloys

This study explores the control of the microstructure and properties of NiTi alloy through the adjustment of 4D printing process parameters. The results indicate that increasing the scanning speed from 450 mm/s to 750 mm/s leads to a change in the phase composition from near full martensitic to a two-phase structure of austenite and martensite. The increase in scanning speed can also reduce the evaporation of Ni element and lower the phase transformation temperature. M s temperature and A f temperature decrease from 93°C and 63°C at 450 mm/s to 37°C and 12°C at 750 mm/s, respectively. Moreover, the scanning speed can alter the texture characteristics and mechanical behavior of NiTi alloy. The hardness value and critical stress increase with the increase in scanning speed, while the strain distribution during tensile deformation becomes uneven at high scanning speed due to the unevenly distributed dual-phase microstructure. These findings provide insights for the optimization of 4D printing parameters to tailor the properties of NiTi alloy for various applications.