Enhancing specific energy absorption of additively manufactured titanium lattice structures through simultaneous manipulation of architecture and constituent material

Abstract

Titanium lattice structures have found a wide range of lightweight applications. However, lattice structures made from the commonly-used commercially pure titanium (CP−Ti) and Ti−6Al−4V exhibit either low strength or post-yielding softening/collapse under uniaxial compression, making them less attractive to energy absorbing applications. In the present work, a series of titanium gyroid lattice structures have been designed and additively manufactured by laser powder bed fusion (L-PBF) to enhance the specific energy absorption (SEA) through manipulation of the architecture and the constituent material. Experimental results show that tailoring the sheet thickness gradient of gyroid lattice structures enables the transformation of the macroscopic deformation mode from hardening followed by softening, which is commonly seen in lattice structures, to continuous hardening. The addition of MgO nanoparticles to CP−Ti feedstock further improves the yield strength through oxygen solute strengthening, while maintaining the continuous hardening behaviour without any post-yielding softening or collapse. As a result, when both sheet thickness gradient and MgO are introduced, the SEA of the uniform gyroid lattice structure is enhanced by approximately 63% due to the combination of continuous hardening behaviour and high strength. Finite element analysis based on the modified volumetric hardening model has been performed to shed light on the underlying mechanism that governs the continuous hardening behaviour. This study demonstrates the tremendous potential of marrying architecture engineering with material design to create high performance lightweight lattice structures by L-PBF.