Page 50 - ESAM-1-2

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

structures, the interfacial region of SS316L/tungsten diffusion of chromium carbide particles into the IN718
exhibited a higher hardness of 543±3.7 HV compared to led to the formation of the Cr C phase, which resulted
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the SS316L and tungsten-rich region, which exhibited in higher hardness at the interface compared to the bulk
392±1.6 HV and 411.7±3.3 HV, respectively. 148 materials. Similarly, the IN718/Cu MMAM structures
This increase in hardness is due to the secondary phases fabricated using MM-LPBF and MM-LDED revealed
like Fe W, Fe W C, and Fe W which disperse high levels enhanced interface hardness. In MM-LPBF, this was
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of hardness due to the presence of brittle and intermetallic attributed to rapid solidification effects from the localized
compound (IMC) phases. In bimetallic structures with laser remelting. 47,184 However, the MM-LDED study did
SS316L as the substrate, it was revealed that the hardness not provide detailed information on the interface or the
mostly exhibited a smooth transition, besides cases having transition in hardness. The studies on Ni/Ti and Ni/Cu
a poor interfacial characteristic (discussed in Section 3), revealed a smooth transition similar to the earlier bimetallic
which has influenced the hardness at the interface by structure observation. In IN718/Ti-6Al-4V, the formation
forming intermetallic phases that have higher hardness of intermetallic phases resulted in superior hardness than
values. the bulk material. These findings further affirm that in
MMAM structures, smooth interfacial transitions can
A similar trend in interfacial hardening has been be achieved even between highly dissimilar materials,
observed in other combinations of MMAM structures. with interfacial hardening predominantly influenced by
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Wei et al. studied the Ti-5Al-2.5Sn/Ti-6Al-4V structures elemental diffusion, intermetallic formation, and process-
and observed a smooth transition at the interface for both specific thermal conditions.
as-deposited and annealed specimens, noting a drop in
overall hardness of the specimen due to the softening In contrast, the hardness at the interface of H13/Cu
effect provided by the “α' → α” recrystallization process. did not exhibit a smooth transition. Instead, it exhibited
Similar to the SS316/CF/IN718 structure, the influence a peak hardness at the interface attributed to the increased
of the IBL in Ti-6Al-4V/SS410 was also significant—with laser hardening, followed by a sudden drop, which was
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the introduction of IBL, such as Nb and NiCr—exhibiting attributed to poor diffusion of elements (Figure 10C).
distinct effects on interfacial hardness. The Ti-6Al-4V/Nb/ Similarly, in CrMn/MS1 bimetallic structures, a mostly
SS410 MMAM structures exhibited a smooth transition smooth transition was observed, but with a sudden
up to the interface with SS410, where the hardness value hardness increase at the interface, resulting from the
dropped due to the element diffusion and heat-affected influence of the presence of MS1. Overall, in the SS316L/
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zone. However, in Ti-6Al-4V/NiCr/SS410, the hardness at P21, SS316L/17-4PH, and CrMn/MS1 MMAM structures,
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the interface was observed to be smoother compared to the a smooth transition from harder to weaker material was
specimens with an Nb IBL. In a Ti/Cu MM composition, revealed, though CrMn/MS1 uniquely exhibited a localized
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it was observed that the hardness of the interface region hardness increase at the interface. In contrast, the H13/Cu
increases with increasing Cu content, primarily due to the bimetallic structure interface deviated significantly from
formation of hard IMCs and solid solution strengthening. this trend, showing a rapid hardness change due to laser
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The transition through the interface in the Ti/Ti and Ti/ hardening in the deposited H13 region and a subsequent
IBL/SS bimetallic structure revealed a smooth transition in drop caused by insufficient interdiffusion.
hardness. In the Ti/Ti bimetallic structure, an overall drop
in hardness was observed due to annealing, while in the Ti/ Additional insight into hardness behavior across
IBL/SS bimetallic structure, the presence of IBL influenced dissimilar materials was observed in Al-based bimetallic
the interfacial region to form a smoother transition with structures. The hardness factors of Al/tungsten, AlSi10Mg/
no abnormalities. C18400, and Al12Si/Al3.5Cu1.5Mg1Si MMAM structures
were analyzed extensively, 172,175 revealing unique
Overall, these studies highlight that the selection behaviors at the interface and during transitioning. In
of IBL and constituent materials in MMAM structures the Al/tungsten bimetallic structure, a smooth transition
critically governs the interfacial hardness profile, with from tungsten (high hardness) to Al (low hardness) was
smoother transitions and tailored mechanical responses observed. In addition, the hardness throughout the
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achievable through strategic material design and thermal sample increased as the scanning speed was reduced
management. (Figure 10D). In AlSi10Mg/C18400, a gradual hardness
Similar to the earlier findings, in the MMAM structures decrease was observed from the Al-rich to Cu-rich regions,
of NiTi/Ti-6Al-4V and IN718/Ti-6Al-4V, a smooth with anomalous hardness values exhibited at the interface.
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transition with no abrupt changes at the interface was Such anomalous hardness values are due to the presence
observed during transitioning. In IN718/Ti-6Al-4V, the of brittle intermetallic Al Cu, which results in hardness
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Volume 1 Issue 2 (2025) 18 doi: 10.36922/ESAM025180010