With the growing interest in additive manufacturing (AM) of metallic materials, several techniques have evolved up to the point of enabling new routes for manufacturing heterogeneous materials tailor-made for specific needs. That is the case of direct energy deposition (DED) manufacturing, whose features are particularly well suited for making functionally graded materials (FGMs). These materials show a gradual change in materials composition — and hence microstructures, properties, and functionalities. FGMs come as a great option when dealing with dissimilar joints or location-specific properties in a bulk part. However, FGM manufacturing is not without flaws and challenges. Apart from common AM-related defects, challenges arise, such as property mismatches or the formation of unexpected phases, which must be addressed.

This document starts by introducing a review of the state-of-the-art in AM of FGMs, addressing their challenges and most impactful case studies, describing the methods and results to date related to the specific materials in this work, and a detailed look at future perspectives. Most of the work in this dissertation falls within the scope of the national collaborative project Multi-FAM (“Development of 3D multi-material and multi-functional parts through AM assisted by intelligent material and process design”) funded by the Spanish Ministry of Science and Innovation (Agencia Estatal de Investigación, Proyectos Retos-Colaboración 2019, RTC2019-007129-5). The project aimed to manufacture 3D printed multi-material parts of particular relevance to the steelmaking industry. The consortium was lead by ArcelorMittal and included AIMEN Technology Centre. IMDEA Materials contributed to the experimental and computational study of material compatibility between the selected alloy systems (AISI SS316L and Inconel 718). To do so, this work combined computational thermodynamic simulations with advanced microstructural and mechanical characterization and other exploratory experimental techniques (e.g. Gleeble physical simulation, X-ray tomography, and neutron diffraction). CalPhaD (Calculation of Phase Diagrams) has been the primary method for thermodynamic simulations to obtain both alloy systems phase equilibrium and properties while also exploring the composition space between them.

These were compared and complemented with several microstructural, mechanical, and thermal characterizations of actual printed FGMs, which were previously optimized and designed for DED manufacturing. The latter part of the dissertation addresses several case scenarios (side projects) in which CalPhaD simulations were used to support other studies, e.g. in the scope of alloy design of High Entropy Alloys (HEAs) for hydrogen storage or high-temperature applications, and master alloys for powder sintering of steels.