Microstructural and mechanical tailoring of PBF-LB/M IN718-based systems through architecture and thermal history control

Laser Powder Bed Fusion (PBF-LB/M) has emerged as one of the most promising additive manufacturing technologies for the production of complex metallic components, offering unprecedented design freedom and enabling the fabrication of architected and multimaterial structures. However, the rapid solidification conditions and highly localized thermal cycles inherent to the process generate microstructures that differ significantly from those obtained through conventional manufacturing routes, making the understanding of processing-microstructure-property relationships essential for the effective design of functional components. This thesis investigates the role of architecture and thermal history in tailoring the microstructural and mechanical behaviour of PBF-LB/M IN718-based systems, with particular emphasis on lattice structures and multimaterial configurations. The work was carried out through a multidisciplinary approach combining mechanical testing, electron microscopy, diffraction techniques and thermal analyses. The first part of the research focuses on the characterization of additively manufactured IN718 lattice structures in the as-built condition. The influence of lattice topology and relative density on the mechanical response was investigated and correlated with the microstructural features generated during the additive manufacturing process. Particular attention was devoted to the relationship between architectural design and deformation mechanisms under compressive loading. The second part addresses the effect of post-processing heat treatments. Starting from the standard heat treatment commonly adopted for conventionally manufactured IN718, an optimization strategy was developed with specific reference to lattice structures. The study demonstrates that the thermal route represents a critical design variable, capable of significantly modifying phase constitution, microstructural homogeneity and mechanical performance. The results highlight that heat treatments originally designed for wrought materials cannot be directly transferred to additively manufactured architectures without considering the unique microstructural state generated by rapid solidification. The third part provides a detailed investigation of phase evolution during thermal processing through a combination of synchrotron X-ray diffraction and transmission electron microscopy. The study clarifies the mechanisms governing Nb redistribution and the formation, dissolution and transformation of secondary phases, including γ′, γ″, δ and Nb-rich constituents. The findings establish a direct link between thermal history, precipitation behaviour and the resulting macroscopic properties. Finally, the research extends the processing–microstructure–property framework to multimaterial systems produced by PBF-LB/M. IN718–GRCop42 structures with different interface geometries and deposition strategies were investigated to evaluate the influence of local thermal conditions on interface formation and microstructural evolution. The results demonstrate that interface morphology, strain accommodation and transition region characteristics are strongly dependent on deposition sequence, interface orientation and local solidification conditions. Overall, this thesis demonstrates that the performance of PBF-LB/M metallic systems cannot be interpreted through isolated variables. Instead, architecture, thermal history and microstructural evolution act synergistically in determining the final behaviour of both lattice structures and multimaterial components. The work provides a comprehensive framework for the design and optimization of advanced additively manufactured metallic systems, contributing to the development of next-generation aerospace and high-performance engineering applications.