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

significant role in determining the metallurgical bonding to another. Although the elemental composition of both
between dissimilar materials. alloys is different, they produced a near-homogeneous
martensitic microstructure due to the high cooling rate.
3.2. Titanium-based bimetallic alloys
In contrast, the interface in a Ti-6Al-4V/SS410
A Ti-6Al-4V/Ti-5Al-2.5Sn bimetallic structure, bimetallic structure observed by Onuike et al. exhibited
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manufactured via MM-LDED and tested by Wei et al., a narrow (15 μm) transition region with numerous cracks
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exhibited high-quality metallurgical bonding, attributed perpendicular to the interface due to the immiscibility
to optimized deposition parameters. Throughout the of SS and Ti alloy. Both materials were discerned by a
entire specimen, defects such as pores, cracks, and lack of thin layer of phase mixture (Figure 6A). To overcome the
fusion were notably scarce, underscoring the efficacy of the immiscibility of Ti-6Al-4V and SS410, niobium (Nb)
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employed parameters and the presence of extremely high and Ni-chromium alloy (NiCr) were used as an IBL to
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thermal gradients along the build direction. In addition, optimize the metallurgical bonding. Ti-6Al-4V/Nb/SS410
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an EDS line scanning profile of the as-built specimen fabricated using MM-LDED showed a good metallurgical
revealed an interdiffusion region spanning 70 μm at the bonding with no cracks or de-bonding. Due to the
interface, with the elemental composition transitioning Marangoni convection, an upward movement of elements
from Tin (Sn)-dominant to Vanadium (V)-dominant. A such as Ti, V, and Nb into the SS410 layer was observed using
strong Marangoni convection allowed the V elements to EDS (Figure 6B). Notably, no brittle intermetallic phases
move downward and the Sn elements to move upward
within the molten liquid. This well-interfacial bonding (e.g., FeTi and Fe Ti) were detected at the IBL, emphasizing
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between dissimilar materials increased its strength the role of Nb as an intermediate bond and diffusion barrier
layer. This highlights its effectiveness in mitigating brittle
compared to Ti-5Al-2.5Sn layers. The physical and thermal intermediate phases and reducing thermal stresses.
properties of Ti-6Al-4V and Ti-5Al-2.5Sn were consistent,
which is evidently represented in the interface bonding, Conversely, in Ti-6Al-4V/NiCr/SS410, a significant
indicating a smooth transition of elements from one side number of pores were observed at the interface,

A

B

Figure 6. Interfacial characteristics of titanium (Ti)-based bimetallic structures. These structures were fabricated using (A) Ti-6Al-4V/NiCr/SS410
MM-laser-directed energy deposition (LDED) and (B) Ti-6Al-4V/Nb/SS410 MM-LDED. The images reveal the interfacial evolution and metallurgical
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bonding behavior across the Ti-base alloy combination with interlayer, with particular emphasis on elemental transition, interlayer strategies, crack
formation, and phase formation. Scale bars: 10 μm, 50 μm, 200 μm, 400 μm, 500 μm, and 0.5 mm. Reprinted with permission from Sahasrabudhe et al.
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(Copyright © 2014, Elsevier B.V.) and Onuike and Bandyopadhyay (Copyright © 2018 Elsevier B.V.).
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Volume 1 Issue 2 (2025) 12 doi: 10.36922/ESAM025180010