Phase Transformation Behavior of NiTi Triply Periodic Minimal Surface Lattices Fabricated by Laser Powder Bed Fusion

Laser powder bed fusion (LPBF) is an appealing additive manufacturing technique suitable for producing intricate products with complex shapes, where traditional subtractive manufacturing methods may be impractical. When dealing with NiTi shape memory alloys, the fabrication process encounters additional challenges due to the material’s high ductility and work hardening characteristics. These properties lead to elevated tool wear and poor workability. However, LPBF overcomes these challenges by eliminating the need for tooling and enabling direct fabrication of complex shapes based on predefined computer-aided designs. Although there has been a growing interest in the LPBF of NiTi in recent years, the fabrication of NiTi structures with architected designs has received limited attention. This study aims to bridge this research gap by investigating the phase transformation behavior of two specific types of triply periodic minimal surface (TPMS) architected NiTi lattices, namely primitive and gyroid, manufactured using LPBF. The study utilized a methodology involving the design of TPMS structures, additive manufacturing, and the characterization of printed samples through electron microscopy, x-ray diffraction, and thermal analysis to measure phase transformation temperatures. The research not only examines the impact of process parameters on the behavior of the fabricated samples but also establishes the influence of cellular geometry on the functional response of TPMS NiTi structures. It was noteworthy to observe that gyroid samples displayed a higher thermal hysteresis and lower reverse transformation enthalpy in comparison with primitive samples.