Effect of PBF-LB process parameters and strut diameter on the microstructure and phase transformation behaviour of Ti-rich nitinol lattice structures

This study examines how volumetric energy density (VED) and lattice strut diameter affect the microstructure, composition, and thermal behaviour of Ti-rich NiTi shape memory alloy lattices produced by laser powder bed fusion (PBF-LB). Lattices with strut diameters of 0.5, 1.0, and 1.5 mm were fabricated across a range of VEDs, and their properties were systematically characterized. Results show that strut diameter critically influences density, Ni evaporation, and transformation behaviour. Thinner struts exhibited higher relative density at low VEDs (98.9% at 31 J/mm 3 ), but increased Ni loss (0.32–0.45 at%) and chemical heterogeneity. Thicker struts exhibited reduced Ni loss (0.28–0.40 at%) and achieved higher maximum densities at mid-range VEDs (99.4% at 42 J/mm 3 ). However, they exhibited increased residual stress resulting in higher thermal hysteresis. The 1.0 mm strut diameter provided the most stable transformation temperatures and lowest thermal hysteresis. These findings highlight the necessity of optimizing both process parameters and geometry to engineer NiTi actuators with tailored functional properties.