Effects of aging heat treatment on the mechanical properties of NiTi triply periodic minimal surface

This study investigated the impact of aging heat treatment time on the mechanical properties of NiTi triply periodic minimal surface structures fabricated through laser powder bed fusion. X-ray diffraction analysis results indicate that with increasing aging time, the NiTi2 phase precipitates while the content of the B19’ phase decreases. At 10 h of aging time, the Ni4Ti3 phase becomes evident in the sample. The differential scanning calorimeter results show that R phase transformation occurs, and the phase transformation temperature increases when the aging time reaches 6 h. Microhardness increases with aging time, peaking at 477.8 HV after 10 h. Compression experiment results reveal a maximum elastic modulus of 1262.82 MPa for the gyroid sheet-shaped structure achieved after 2 h. In addition, the superelasticity test indicates the highest recoverable strains at 2%, 4%, and 6% compressive strain for the gyroid rod-shaped structure after aging for 10 h. In cyclic compression experiments, the ratio of shape memory recovery increases from 40% at 0 h to 97% at 6 h. Fracture analysis results show that the transition in the fracture mechanism from brittle fracture to quasi-cleavage fracture occurs after aging heat treatment.