Microstructure and Mechanical Properties of NiTi Shape Memory Alloys by Laser Engineered Net Shaping

Herein, NiTi alloys are prepared by laser engineered net shaping (LENS) technology. By exploring the mechanical properties and microstructures of NiTi samples under different laser powers, it is concluded that NiTi alloys with a laser power of 350 W have better tensile strength (783 MPa) and strain recovery rate (59.01%). In addition, the mechanical properties and microstructure of NiTi samples with a laser power of 350 W at different aging temperatures (400-800 degrees C) are also explored. It is found that NiTi alloys aged at 600 degrees C had better tensile strength (729 MPa) and strain recovery rate (92.85%). In addition, the phase-transition temperature and endothermic enthalpy and exothermic enthalpy of the NiTi samples after thermal treatment increased, which is attributed to the formation of stable martensite (B19 ') inside the NiTi samples after thermal treatment, and the type of internal NiTi phases structure change significantly. Thermal treatment can generate Ni4Ti3, NiTi2 precipitates, and martensite (B19 ') with high density of dislocations inside the NiTi samples. Herein, it is showed that LENS can prepare NiTi alloys with excellent mechanical and structural properties by controlling the equipment parameters and aging temperature.