Page 45 - ESAM-1-2

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

attributed to the inadequate energy input during NiCr A
layer deposition. Nevertheless, Ti-6Al-4V/NiCr has
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amalgamated and formed a strong overall bonding, as
evidenced by the presence of light and darker circles, as
observed in Figure 6A. The disparity in thermal properties
between Nb and NiCr contributes to the observed porosity
in Ti-6Al-4V/NiCr/SS410 but not in Ti-6Al-4V/Nb/SS410.
This underscores the importance of material compatibility
and thermal characteristics when selecting intermediate
materials. Another interesting investigation looked at the
effect of transition joints on the interfacial characteristics B
in Ti-6Al-4V/TiC. Using dual-material transition joints,
two distinct joints - (1) Butt joint and (2) interlock
joints illustrated a crack-free interfacial bonding.
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These findings shed light on the effectiveness of different
joint configurations in achieving a strong and seamless
bond, providing valuable insights toward the design and
fabrication of dual-material transition applications. Owing
to the similar physical and thermal properties of Ti-6Al-4V Figure 7. Interfacial characteristics of nickel (Ni)-based bimetallic alloys
and TiC, the resulting bonds exhibited defect-free surfaces fabricated through multi-material laser powder bed fusion (MM-LPBF)
and microstructural characteristics resembling those and mixed-material laser-directed energy deposition (MM-LDED).
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observed in Ti-6Al-4V/Ti-5Al-2.5Sn joints. (A) IN718/SS316L produced by MM-LPBF and (B) IN718/Ti-6Al-4V
produced by MM-LDED. The images reveal minor crack formation,
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metal lump formation, and delamination at the interface across different
3.3. Nickel-based bimetallic alloys material combinations and process techniques. Scale bars: 10 μm and
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Bimetallic structures of IN718/SS316L and IN625/ 50 μm. Reprinted with permission from Onuike and Bandyopadhyay
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SS316L, fabricated using MM-LPBF and MMLDED, (Copyright © 2018 Elsevier B.V.) and Duval-Chaneac et al. (Copyright
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© 2021 Elsevier Ltd.).
respectively, exhibited similar wavy characteristics at the
interface. These distinctive characteristics are caused by
the high degree of molten pool banding, compared to the layer was introduced, which facilitated improved bonding
interface between SS316L/IN625, as explained in Section by gradually bridging the thermal and physical mismatches
3.1 (Figure 4C, D, and F). The interface exhibited epitaxial between the dissimilar alloys. This approach highlights
growth, implying that irregular-shaped coarse grains are the effectiveness of using a gradient transition layer in
observed at the transition/composite zone. At the IN718/ overcoming bonding challenges in systems with significant
SS316L interface, Duval-Chaneac et al. observed a property disparities.
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minor crack formed due to liquation cracking (Figure 7A). Similar to previous studies, the interfacial characteristics
Liquation cracking occurs due to the rapid solidification of IN718/Ti-6Al-4V and NiTi/Ti-6Al-4V were observed
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of alloys with high alloying content, which widens the to form lateral cracks with no visible crack formation. The
solidification range and promotes the formation of lateral crack formation at the interface between IN718/
liquation cracks. Notably, both Ni-based systems exhibited Ti-6Al-4V was due to the larger dissimilarities in CTE
interfacial cracks resulting from solidification-induced and immiscibility, which inhibit bonding; the crack
stresses and the absence of compensating melt flow. In was later overcome by introducing a vanadium-carbide
contrast, a Ni/Cu bimetallic structure demonstrated poor compositional bonding layer (Figure 7B). Vanadium-
metallurgical bonding, with strong interfacial adhesion carbide serves as a bonding link for dissimilar materials and
between the two alloys. The high thermal conductivity of minimizes the formation of brittle intermetallic phases.
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Cu allowed deeper penetration into the Ni-based substrate, However, due to the close range in thermal properties
promoting diffusion and metallurgical integration. Onuike between NiTi and Ti-6Al-4V and NiTi’s secondary
et al. examined IN718/GRCop-48 bimetallic structure dominant composition being Ti-element, the interface
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fabricated using LDED and observed poor interfacial exhibited good metallurgical bonding. Bartolomeu et al.
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bonding, characterized by metal lump formation and the indicated that, due to the MM-LPBF fabrication strategy
balling phenomenon. This was attributed to the extreme (removing excess powder before adding Ti-6Al-4V) along
differences in thermal properties and poor diffusion with adequate process parameters, the number of cracks
compatibility. To address this, a compositional gradient was reduced, and good metallurgical bonding was achieved.

Volume 1 Issue 2 (2025) 13 doi: 10.36922/ESAM025180010