Directed energy deposition (DED) additive manufacturing systems have been developed and optimized for typical engineering materials and operational requirements. However, parts fabricated via DED often demonstrate a diminished material response, encompassing inferior mechanical properties and heat treatment outcomes compared to traditionally manufactured components (e.g., wrought and cast materials). As a result, parts produced by DED fail to meet stringent specifications and industry requirements, such as those in the nuclear, oil and gas, and aeronautics sectors, potentially limiting the industrial scalability of DED processes. To address these challenges, systems integrating DED with interlayer (cold or hot) mechanical deformation (e.g., rolling and hammering/peening, forging) have been developed. These systems refine the microstructure, mitigate the typical crystallographic texture through static and/or dynamic recrystallization, and enhance mechanical properties and heat treatment responses without altering material specifications. In this regard, the present state-of-the-art review reports the DED + interlayer mechanical deformation systems and their variants, and their potential and limitations, providing a critical analysis to support the development and adaptation of this technology to overcome the process and material limitations that currently prevent the large-scale industrial adoption of DED processes. Furthermore, a detailed description of the grain size refinement mechanisms induced by interlayer mechanical deformation and their respective effects on the mechanical properties of commonly used 3D-printed engineering alloys (e.g., Ti-6Al-4V, Inconel 718, various low-alloy steels, AISI 316L stainless steel, and Al-based series 2xxx) is comprehensively analyzed.

9%Ni steel was recently used for the first time in the field of injection unit (IU) for the injection of CO₂ into oil wells. Because such steels are operated in H₂S medium and are susceptible to sulfide stress cracking, their pipes are cladded with Ni-based superalloy 625 by using gas tungsten arc welding with a hot wire to prevent this phenomenon from occurring. The transition zone of substrate/clad can have high hardness and low toughness, and promote failure of the component during service; therefore, it is very important to know its characteristics. In this work, this transition zone was analyzed through optical and scanning electron microscopy with energy dispersive X-ray spectrometry and electron backscatter diffraction, as well as Vickers microhardness, shear and bend tests. Metallographic analysis identified type I and II boundaries with distinct chemical gradients, MC-type carbides, Laves/γ eutectics, peninsulas macrosegregation, crystallographic texture close to in the clads, residual strain, and drop of microhardness across the transition zone. The clads were approved in the shear and bend tests. This work proposes a new type II boundary formation mechanism in dissimilar welds of steels that do not exhibit the allotropic transformation δ → γ during the welding thermal cycle and do not experience a change in the solidification mode.

Functionally Graded Materials (FGMs) can outperform their homogeneous counterparts. Advances in digitalization technologies, mainly additive manufacturing, have enabled the synthesis of materials with tailored properties and functionalities. Joining dissimilar metals to attain compositional grading is a relatively unexplored research area and holds great promise for engineering applications. Metallurgical challenges may arise; thus, a theoretical critical analysis is presented in this paper. A multidisciplinary methodology is proposed here to unify optimal design, multi-feed Wire-Arc Additive Manufacturing (WAAM), and image-based characterization methods to create structure-specific oriented FGM parts. Topology optimization is used to design FGMs. A beam under pure bending is used to explore the layer-wise FGM concept, which is also analytically validated. The challenges, limitations, and role of WAAM in creating FGM parts are discussed, along with the importance of numerical validation using full-field deformation data. As a result, a conceptual FGM engineering workflow is proposed at this stage, enabling digital data conversion regarding geometry and compositional grading. This is a step forward in processing in silico data, with a view to experimentally producing parts in future. An optimized FGM beam, revealing an optimal layout and a property gradient from iron to copper along the build direction (bottom–up) that significantly reduces the normal pure bending stresses (by 26%), is used as a case study to validate the proposed digital workflow.