Tailored pore canal characteristics and compressive deformation behavior of bionic porous NiTi shape memory alloy prepared by selective laser melting

Inspired by the Bouligand structure within the crab claw, the NiTi-based bionic helicoidal porous part was fabricated based on selective laser melting (SLM). The helicoidal porous structure (HPS) was created by controlling the geometric characteristics and distribution of metallurgical pore canals within the part. The compressive deformation behavior of the metallurgical pore canal was disclosed. It was shown that the metallurgical pore canals kept the same deformation feature as the whole HPS at an early period (800 MPa) and then experienced a rapid transformation from completely recoverable state to completely unrecoverable state, with the applied stress level increasing. When the sample came to break, a zigzag fracture edge was found, indicating a twisting propagation path of a crack. Influence of laser processing parameter on the pore canal characteristic and quasi-static compressive behavior of the HPS was evaluated in details. The metallurgical pore canals with three different kinds of cross-sectional configurations were obtained at different laser processing parameters. As the larger layer thickness d together with the smaller hatch spacing h was applied, the pore canal tended to become more applanate. In this condition, the experiment and simulation results suggested that stress concentration emerging nearby the pore canal became more significant during the compression, consequently leading to a deteriorative superelasticity due to an increase of residual strain after unloading, as well as an early failure of the sample. (paper)