Page 51 - ESAM-1-2

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

ranges of 400 – 600 HV. In Al12Si/Al3.5Cu1.5Mg1Si combinations fabricated using Cu alloys such as
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MMAM structures, the interfacial region showed a sudden CuSn10 58,139,183 and C18400. Chen et al. manufactured
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drop in hardness moving away from Al12Si. From the SS316L/CuSn10 specimens in both Type-A and Type-D
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silicon-dominant region (zone II) to the Cu-dominant orientations. In both cases, the tensile strength and
region (zone III) (Figure 10E), the hardness increased elongation were lower than those of bulk SS316L, with
significantly. This was attributed to the microstructural UTS values of 423.3 ± 30.2 MPa and 459.1 ± 8 MPa,
shift from cellular to granular morphology, accompanied and elongation values of 4.6 ± 0.9% and 10.5 ± 1.7%,
by the development of a <001> fiber texture. Beyond zone respectively. Type-D specimens exhibited slightly higher
III, however, the hardness decreased again due to grain UTS and approximately 6% greater elongation than Type-A
growth and increased silicon content. specimens (Figure 11A). Fractography revealed distinct
fracture modes: Type-A specimens exhibited cleavage
4.2. Tensile strength fracture (a brittle transgranular mode) at the interfacial
Analyzing the tensile strength of MMs is necessary to layer, attributed to unmelted SS316 powder particles,
determine the tensile characteristics at the interface and whereas Type-D specimens demonstrated a mixed mode
the bond between the dissimilar metals based on the of transgranular and intergranular fracture, with brittle
deposition order and design. This section delves into fractures concentrated at the fusion zone.
the tensile properties of MMAM structures, where the Liu et al. reported similar trends for Type-A
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dissimilar material deposition configurations are classified orientation, although they observed lower tensile strength
with respect to the build direction as Types A, B, C, and than that reported by Chen et al., primarily due to the
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D, as shown in Figure 9. For the ease of the readers, the presence of pores and interfacial cracks. A comparative
discussion follows the same order as Section 3, beginning study between LPBF and laser-welded structures indicated
with SS-based to Cu-based bimetallic structures. that LPBF showed higher tensile stress, attributed to finer
The tensile strength of SS/Ni bimetallic structures has grain structures formed under higher cooling rates. 139
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been evaluated using different compositions of Ni-based Compared to SS316L/CuSn10, the tensile strength of
alloys, such as IN625 133,157 and IN718. For SS316/ SS316L/C18400 in Type-D orientation was lower (310 ±
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IN625 structures fabricated in the Type-A orientation, 18 MPa. However, unlike in previous SS/Cu bimetallic
Feenstra et al. and Ahsan et al. used MM-LDED and systems, the fracture occurred on the Cu-side (the weaker
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MM-WAAM, respectively. In both cases, the UTS was material), indicating a well-formed metallurgical bond.
found to be greater than that of wrought and as-built SS316, Between CuSn10 and C18400, the latter showed improved
with the bimetallic structures exhibiting a UTS of 577 ± bonding with SS316L, likely due to the lower reactivity of
16 MPa. Interestingly, elongation values ranged from 10 – Fe–Cr compared to Fe–Sn. The Fe–Sn system is prone to
15% in MM-LDED to 40% in MM-WAAM. Both studies form brittle intermetallic phases such as FeSn . In addition,
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reported dimple-like features on the fracture surfaces, Type-D orientation marginally performed better than
suggesting ductile failure through micro-void coalescence. Type-A, which may be attributed to the larger bonding
For SS316L/IN718 fabricated in Type-A orientation using area of Type-D.
MM-LPBF, UTS and elongation values were 596 ± 10 MPa Extending beyond Cu-based bimetallic, SS316L has
and 28.1%, respectively—higher UTS than AM-SS316 but also been combined with dissimilar materials such as W
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lower elongation than AM-IN718. Post-fracture analysis and Ti-6Al-4V, yielding varied interfacial characteristics.
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of the fracture surface revealed similar features to SS316/ In MM-LPBF-fabricated SS316L/W (Type-D) structures,
IN625, with dimple-like characteristics leading to a mixed- tensile strength increased from 239.7 MPa to 257.4
mode fracture, where the ductile mode was prominent. In MPa after heat treatment, while elongation improved
both bimetallic structures, UTS values exhibited similar significantly from 5.3% to 17%. This improvement was
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trends with a variation of 19 ± 19 MPa, and elongation attributed to the transformation of the brittle fracture
remained within a comparable range. The root cause of mode to a more ductile one, driven by the formation of
failure in both cases was the formation of micro-voids at Fe W near the interface—an inherently hard and brittle
the interface, leading to ductile fracture and lower UTS phase. Fractures typically initiated on the W side of the
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compared to monolithic Ni-based alloys. Mitigating interface. For SS316L/Ti-6Al-4V (Type-A) MM-LPBF
interfacial micro-voids could potentially enhance the structures, in which a Cu-alloy was used as an IBL, the
mechanical performance of bimetallic structures. scanning speed was a key parameter. Tey et al. observed
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Extending the evaluation to SS/Cu bimetallic that specimens built at 650 mm/s exhibited higher tensile
structures, researchers have investigated various strength and better bonding than those built at 350 mm/s.

Volume 1 Issue 2 (2025) 19 doi: 10.36922/ESAM025180010