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

MMAM, is provided in Section 2. Using these processes, in propulsion, heat exchangers, and other components.
the transition between dissimilar materials can be either For instance, in 2017, the National Aeronautics and
discrete or gradual. Space Administration launched the “Rapid Analysis
The interfaces of MMAM structures consist of either and Manufacturing Propulsion Technology” program
a discrete boundary (discrete MMAM), characterized by to reduce the cost and weight of the thrust chamber
a direct transition between two materials; a functionally assembly. This initiative utilized bimetallic joints to
graded boundary—in which the proportion of material directly fuse the copper (Cu) combustion chamber
composition varies along the interface—or a discrete with the nickel (Ni) alloy nozzle, eliminating the need
boundary incorporating a third material as an interlayer, as for additional fasteners. Cu/Ni alloy combinations are
shown in Figure 2. Functionally graded materials (FGM) particularly suitable for propulsion applications due to
enable complex and locally controlled MM component the high thermal conductivity of Cu and the mechanical
fabrication by providing smooth transitions between strength of Ni. 45-47 Another MMAM demonstration in
dissimilar materials. However, FGM comes with limitations, industry integrated titanium (Ti) and aluminum (Al)
such as inconsistent gradient control and unpredictable to manufacture a lightweight yet corrosion-resistant
feedstock deposition, which may limit the repeatability and spaceflight frame, capitalizing on Ti’s high corrosion
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precision of the FGM components. In contrast, discrete resistance and Al’s lightweight. Another example of
MMAM with direct compositional change (including MMAM application is the Cu/stainless steel (SS) MMAM
adaptation of interlayer material) offers significant heat exchanger fabricated by Aerosint (Belgium),
engineering benefits such as increased flexibility in design where complex Cu channels were embedded in SS to
and production, property optimization, and the ability to produce a monolithic structure that demonstrated a
realize complex functionalities. 42,43 Both FGM and discrete relatively higher cost-effectiveness over conventional
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MMAM components can deliver localized enhancements, manufacturing. Similarly, an SS/Ni component was
such as high wear resistance, high-temperature resistance, manufactured through MMAM for a heat exchanger by
and corrosion resistance in target regions, while leveraging the high-temperature performance of Ni and
maintaining traditional mechanical properties at adequate the higher ductility, corrosion resistance, and lower cost
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level, an approach that is often restricted in single-material of SS. The applications of MMAM in aerospace have
components. 40,44 For the reader’s ease, the term MMAM extended to vital components such as propulsion systems,
will now be used interchangeably with discrete MMAM heat exchangers, and spacecraft body frames without
to identify a discrete compositional change between compromising functional performance.
dissimilar materials using AM here on. The impact of MMAM extends beyond the aerospace
The adoption of MMAM has garnered increasing industry. With the growing adoption in the automotive
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interest across industries such as aerospace, 22,45-49 industry, components such as electric motor rotor and car
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automotive, 50,51 biomedical, and nuclear energy. 53,54 In the chassis have been fabricated using MMAM techniques
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aerospace industry, MMAM implemented functionality with iron (Fe)/Ni and Al/SS compositions, respectively.
The design flexibility enabled through LPBF allowed for the
reduction of eddy currents and increased motor efficiency.
Meanwhile, the Al/SS MMAM chassis helped reduce the
vehicle’s weight while maintaining higher strength and
corrosion resistance. Similarly, to the automotive industry,
the biomedical fields, nuclear energy, 53,54 and anti-
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counterfeiting have implemented MMAM. The MMAM
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of Ni/Ti has been explored as a viable hip implant due to
its shape memory behavior and bio-compatibility. In the
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nuclear energy industry, tungsten/Cu has been explored
for use in fusion nuclear reactor components, leveraging
their combined high-temperature resistance and excellent
plasma radiation resistance properties. 53,54 Besides the
large-scale industries, MMAM has shown promise in anti-
Figure 2. Schematic illustration of bimetallic, functionally graded counterfeiting, where embedded safety features, such as a
materials, and interlayer-assisted multi-material additive manufacturing quick response code, have been incorporated into metallic
structures, highlighting the differences in materials transition and
material compositional distribution characteristics across the interface components made of SS/Cu alloys to allow traceability and
Abbreviation: Comp.: Composition. authentication. 55

Volume 1 Issue 2 (2025) 3 doi: 10.36922/ESAM025180010