Additive manufacturing has found its niche in the manufacturing industry. It has become a widespread technology encompassing a vast range of feedstock materials. The ability to manufacture near netshape end components combined with unprecedented design freedom brands additive manufacturing as a convenient technique to fabricate sophisticated components in high-end industries such as aerospace, automotive and biomedicine. An example of such sophisticated components is a lattice structure, which possess a high strength to weight ratio and is exceptionally useful for light-weighting
and energy absorption.

Strut-based lattice structures are characterized by a three-dimensional periodic topological arrangement of beams. The mechanical behaviour of the lattice structures is categorized as either bending-dominated, which features a very compliant and homogeneous response, or stretch dominated, which is characterized by periodic oscillations in the plastic stress occurring due to strut collapse along specific planes. Until recent times, the topology of the lattice was considered the
primary factor determining the mode of collapse of the lattice structures, as captured by the classical Maxwell’s criterion and the Gibson-Ashby model.

This research aims at investigating the effect of the microstructure of the base material, coupled with the topology, on the mechanical behaviour of additively manufactured lattice structures. In the first part, the effect of two different microstructure states, i.e., precipitated versus solid solution, on the mechanical behaviour of body centred cubic (BCC), face centred cubic (FCC) and hexagonal close x packed (HCP) single crystalline Inconel 718 lattice structures fabricated via laser powder bed fusion, is analyzed. Secondly, the influence of the base material microstructure on the efficacy of hybridization
by the introduction of meta-precipitates, is reported. The phenomenon of dynamic strain aging in the lattice structures is investigated as well at the end.

This thesis effectively pinpoints the crucial role of the base material microstructure on the mechanical behaviour of the lattice structures. In particular, precipitation is observed to induce a transition in the mechanical behaviour mode from bending-dominated to stretch-dominated, which is rationalized based on the alteration of the strut deformation mechanism. The study also reports an optimal metaprecipitate distribution to enhance the mechanical performance of hybrid lattice structures, highlighting hybridization as an effective mean to improve the strength of the lattice structures with a controlled deformation response. Lastly, the research puts forth the novel observation of the topology of the lattice dictating the occurrence of dynamic strain aging in the lattice structures. The research globally attests that the synergistic effect of microstructural features and unit cell topology widens the avenue of design of lattice structures with exceptional properties.