Laser additive manufactured NiTi-based bioinspired helicoidal structure with excellent pseudoelasticity and energy absorption capacity

Functionality-driven biomimetic additive manufacturing (AM), as a research hotspot of 3D printing field, is providing unprecedented opportunities for developing next-generation functional materials in mechanical, electrical, optical and biomedical engineering. In this work, we developed a laser AM-ed NiTi-based helicoidal structure with excellent pseudoelasticity and energy absorption capacity, inspired by the biological architecture in the exoskeleton of the crab's claw. The rotation angle theta corresponding to the misorientation of rods in adjacent layers, as the key structure parameter, was involved into the investigations on the forming quality, pseudoelastic response and fracture behavior of the laser AM-ed helicoidal structures. The results showed that an increase in theta could improve the forming accuracy of rods but decrease the porosity due to the formation of more closed pores filled with unmelted powder particles. These pores formed by the helically stacked rods had sharp edges that could trigger earlier stress concentration and phase transformation or even strain hardening during the loading process. In views of more uniform stress distribution, the helicoidal structure with theta = 36 degrees exhibited the largest recoverable strain of 4.32 %. Regarding the deformation and fracture behavior, it was found that the helicoidal structures with small theta were inclined to exhibit an auxetic deformation behavior and a sluggish fracture process, while the ones with larger theta were prone to a buckling deformation mode and a sudden failure. Furthermore, all helicoidal structures presented excellent energy absorption properties in terms of both unit volume and unit mass values, which could be attributed to the cross-scale hierarchical structures.