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Engineering Science in
Additive Manufacturing Multi-material additive manufacturing of metals

1. Introduction A

Metal additive manufacturing (AM) is revolutionizing
1,2
industries with its growing adoption across automotive,
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6-9
nuclear, aerospace, energy, 10-12 and biomedical F B
sectors. 13-18 Utilizing a layer-by-layer approach guided
by computer-aided design models, metal AM offers
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transformative advantages over traditional manufacturing
methods, including reduced material waste, accelerated
production cycles, enhanced part consolidation, and
unprecedented design flexibility. While significant strides E C
have been made in fabricating single-material components,
the next frontier lies in further advancing multi-material
(MM) metal AM (MMAM). Enhancing the quality,
reliability, and performance of MM components is critical D
to unlocking their full potential and meeting the rigorous
demands of real-world applications—a challenge this
review seeks to address following a roadmap consisting of
six topics, as presented in Figure 1.
Recent advancements in AM have enabled the
processing of multiple materials within a single build, Figure 1. Road map for the future of bimetallic multi-material additive
a technique referred to as MMAM. Components manufacturing (MMAM). Includes the discussion on (A) alloy
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manufactured using MMs can produce tailored compatibility. Reproduced with permission from Sun et al. Copyright©
Elsevier 2020. (B) Powder recyclability and contamination, (C) AM
mechanical properties according to spatial part design in-process monitoring techniques. Reproduced with permission from
requirements, and concurrent local material assignment He et al. Copyright© Elsevier 2023. (D) MMAM process engineering,
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and processing conditions. In addition to the tailored (E) MMAM mechanical testing standardization, and (F) modeling and
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mechanical characteristics, the MMAM approach also simulation. Reproduced with permission from Aerosint Company and
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enables manufacturing complex structures that are Gu et al. Copyright © Elsevier 2020.
otherwise cost-prohibitive or often not feasible through that have been proven for single metallic materials and are
other manufacturing methods. 24-30 Recent advancements under rapid development for MMAM. The list includes
in material deposition have enabled AM users to achieve three main processes: (i) Laser-based powder bed fusion
precision control at the voxel length scale in the order (LPBF) and electron-beam powder bed fusion (EB-PBF),
of a few hundred microns. 31,32 By leveraging the existing (ii) laser-directed energy deposition (LDED), and (iii)
advantages of AM processes, ongoing advancements wire-arc AM (WAAM). Among these, LPBF is known
in MM would introduce a new paradigm and range of for achieving higher dimensional accuracy; however, it
opportunities for design, mechanical properties, and suffers from small build volumes, low surface roughness,
manufacturing capabilities. 33
and low production efficiency. These drawbacks result
Despite the numerous advantages of MMAM, from factors such as fine powder particles (10 – 50 μm),
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limitations in the detailed understanding of the process– relatively large laser spot size (50 – 80 μm), small layer
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structure–property (P-S-P) relationships present thickness (<100 μm), and a high risk of powder cross-
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severe constraints in fully adopting and leveraging its contamination. 38-41 In Section 2.1, the author will discuss in
capabilities. Some examples of the critical challenges faced depth the advantages and limitations of LPBF. In contrast,
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by MMAM include the complex behavior at the interfaces LDED and WAAM offer significant advantages in terms
of the dissimilar materials, heterogeneous thermal of higher deposition rate, minimal cross-contamination
properties (melting temperature, thermal conductivity, between multiple materials, and suitability for large-scale
laser absorptivity, and coefficient of thermal expansion component manufacturing. However, these techniques
[CTE]), and cross-contamination between virgin and used are associated with high surface roughness and low-
powders. Addressing these gaps is essential for qualifying dimensional accuracy (100 μm). Given these trade-
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MMAM for high-performance applications in aerospace, offs, recent progress has focused on leveraging all three
defense, energy, biomedical, and other emerging industries. process techniques for the fabrication of MM components.
To effectively address these challenges, it is vital to A detailed description of each process and the mechanics
examine the most widely adopted metal AM processes of melt pool formation, as well as alloy compatibility in

Volume 1 Issue 2 (2025) 2 doi: 10.36922/ESAM025180010