Optimization of repetitive energy absorption properties of LPBF NiTi porous structures by compositional gradient design

NiTi porous structures fabricated by laser powder bed fusion (LPBF) exhibit significant potential for application in repetitive energy absorption scenarios. However, the existing NiTi porous structures typically exhibit stress concentration, which limits their repetitive energy absorption performance. In this paper, a compositional gradient design method based on LPBF is proposed. The gradient NiTi honeycombs with a gradient distribution of Ni content, phase transition behaviour, microstructure and mechanical properties are prepared. The energy absorption and shape recovery properties of gradient NiTi honeycombs under cyclic loading-unloading-heating are investigated. The findings demonstrate that the LPBF-based compositional gradient design method can effectively regulate the local stress distribution and deformation behaviour of the NiTi porous structure without altering its geometrical shape, thereby enhancing its repetitive energy absorption performance. In addition, a Ni evaporation prediction model has been developed to elucidate the controlling mechanism of process parameters on Ni evaporation in the melt pool. Furthermore, the influence mechanism of gradient distribution on the stress distribution and deformation behavior of NiTi honeycombs is explored. This study proposes a novel approach for the regulation and optimization of the repetitive energy absorption properties of NiTi porous structures, thereby further expanding their design space.