Achieving multiple effects of 3D-printed NiTi-based alloys via laser beam manipulation and their mutual collaboration for heat-driven elastocaloric cooling

NiTi alloys can be made to demonstrate multiple effects including the shape memory effect (SME), superelastic effect (SE), and elastocaloric effect (eCE), by finely tailoring the Ni content. Notably, laser 3D printing technology has shown great potential for manufacturing NiTi alloys with tunable Ni contents and different phase transformation temperatures (TTs) by changing the laser energy input. Hence, through processing-parameter design, laser 3D-printed NiTi alloys with various functional behaviors can be achieved. This, in turn, potentially enables the rapid prototype manufacturing of a compact multi-effect coupled heat-driven elastocaloric cooling device. However, the mechanisms governing functional differentiation using this technology remain unclear. This study evaluated the integration of laser 3D printing technology and a microstructure-derived functional differentiation strategy to verify the feasibility of heat-driven elastocaloric cooling. By strategically manipulating the laser power (P) and scanning speed (v) across 30 parameter sets, we achieved a precise functional differentiation of NiTi alloys from a single pre-alloyed powder. A comprehensive functional map in the P-v plane was established. It delineates the regions dominated by room-temperature SE/eCE or SME. NiTi alloys processed with a low-energy input excel as superelastic refrigerants, whereas those fabricated with a high-energy input are ideal thermal actuators. Furthermore, the physical mechanisms underlying this tunable functional behavior were revealed through detailed microstructural characterizations. This work has provided a fundamental and practical framework for laser 3D printing of functionally graded NiTi components, thereby paving the way for the development of compact, self-driving, and efficient elastocaloric cooling systems.