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

A D G J

B E H K

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Figure 3. Summary of discrete multi-material (MM) additive manufacturing (MMAM) processes, interfacial characterization techniques, mechanical
properties characterization, and industrial applications. (A-C) The three common methods of metal MMAM are MM-LPBF, MM-DED, and MM-WAAM.
(D-F) Common methods of interfacial characterization, namely scanning electron microscopy, energy dispersive spectroscopy, and electron backscatter
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diffraction, respectively. Scale bar: 100 µm. Reprinted with permission from Bai et al. and Wei et al. (G-I) Methods of mechanical characterization of
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MMAM structures through indentation hardness testing and tensile testing with variations in material orientation. Reprinted with permission from
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Bai et al. and Chen et al. . Copyright© Elsevier 2019. (J-L) Space applications of MMAM designs. 49,59,23 Reprinted with permission from Wessel and
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Amsterdam, Schneck et al., and Gu et al. Copyright© Elsevier 2021.
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and smaller layer thickness (<100 μm). Limitations of (Figure 3B). These nozzles can be mounted onto a multi-
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MM-LPBF include (i) limited build size, (ii) challenges in axis arm that moves around a fixed component or onto
powder recyclability, and (iii) dependence on powder size a tool head to deposit onto a component mounted in a
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and processing parameters. five-axis vice. Given these capabilities, MM-LDED offers
unique advantages and limitations, as summarized below.
2.2. Laser-directed energy deposition
Advantages of MM-LDED include (i) inherent
Laser-directed energy deposition is defined as an “AM functionality of depositing MM and location-specific
process in which focused thermal energy is used to fuse material deposition, 88,89,91 (ii) higher rate of deposition rates
materials by melting as they are being deposited” by the compared to PBF, 88,92,93 (±2.5 kg/h for LDED vs. ±0.01 kg/h
ISO/ASTM 52900 standard. The LDED process deposits for LPBF vs. ±0.25 kg/h for EB-PBF), (iii) large-scale
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powder feedstock directly onto the substrate by melting fabrication (compared to LPBF), 92,93,95 and (iv) potential
it in a controlled heated region using focused energy in use for coating, cladding, 96,97 and repairing damaged
the form of a laser, electron beam, or plasma arc. 88,89 The parts. 98,99 Limitations of MM-LDED include (i) limited
process of feeding molten powder or wire feedstock into design freedom due to lower-dimensional accuracy and
a melt pool produced by the heat source beam builds higher surface roughness, 95,100 (ii) low powder efficiency
material onto the substrate in a layer-wise process, followed and recyclability, particularly in MM, and (iii) possible
by rapid solidification. The feedstock can be changed mid- shrinkage, residual stress, and deformation due to thermal
process to produce discrete or graded heterogeneous process cycling. LDED is commonly paired with computer
components with tailored material properties. Inert gases numerical control machining as a hybrid-AM solution to
are used during the AM process to prevent the molten pool resolve the poor surface finish and achieve near-net shape
from being contaminated by unmelted powder particles or geometry. 93
porosities. In multi-material LDED (MM-LDED), the
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fabrication process follows the same method as a single- 2.3. Wire arc AM
material LDED with the inclusion of dissimilar materials Wire arc AM is a subset of LDED that uses a welding arc
through powder ejecting nozzle from different hoppers to generate a melt pool. WAAM is gaining more interest
Volume 1 Issue 2 (2025) 5 doi: 10.36922/ESAM025180010