Ti-6Al-4V hollow-strut lattice materials by laser powder bed fusion

Abstract

Hollow-strut metal lattices are an emerging class of cellular metallic materials. However, their mechanical properties at relative densities (ρRD) higher than 10% are largely unknown because conventional manufacturing methods are ill-equipped to fabricate them. In this study, face-centered cubic (FCC) and FCC with Z-struts (FCCZ) Ti-6Al-4V hollow-strut lattices with ρRD = 8-16% are fabricated using laser powder bed fusion (LPBF) additive manufacturing (AM). Both lattice topologies exhibited yield strength (σ⁎) and elastic modulus (E⁎) at the upper empirical limits for solid-strut metal lattices with similar ρRD values. Furthermore, the difference in σ⁎ or E⁎ between hollow-strut FCC and FCCZ lattices is much smaller than that between solid-strut FCC and FCCZ lattices. The deformation behaviours and failure modes of the manufactured Ti-6Al-4V hollow-strut FCC and FCCZ lattices were investigated by uniaxial compression and finite element modelling (FEM). In addition to their lattice topology, the very fine (~20 μm) equiaxed prior-β grains in the Ti-6Al-4V hollow-strut thin walls further contribute to their superior mechanical properties, compared with the coarse columnar grains in Ti-6Al-4V solid-strut lattices. Finally, the manufacturability established in this work provides a reliable pathway for LPBF-AM of Ti-6Al-4V hollow-strut lattices. The findings of this work are expected to apply to other hollow-strut lattice topologies.