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Materials Science in Additive Manufacturing LPBF of Ti-Al-graded multi-materials

through traditional fabrication methods such as bolting interface. Consequently, the rapid solidification process
and welding. However, these methods are susceptible to in LPBF induces the development of thermal stress and
issues such as fatigue and looseness under high-frequency microcracks at the interface. Wei et al. successfully
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vibrational environments, imposing substantial limitations utilized a composition-graded layer to fabricate
on the geometric shapes of the parts and leading to interface 316L/CuSn10-graded multi-material parts with excellent
defects and brittle phase issues that severely compromise metallurgical bonding. They discovered that elements
the reliability of the parts, ultimately affecting their service at the interface exhibited good mutual diffusion, and
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life. Employing graded multi-material design is expected microhardness showed a graded change along the building
to achieve integrated fabrication of “material-structure- direction. The results indicated that a composition-graded
performance” in Ti6Al4V/AlMgScZr frame girder to layer could help reduce the temperature gradient between
achieve excellent interfacial metallurgical bonding and 316L and CuSn10, alleviate thermal stress, significantly
comprehensive mechanical properties. 6 inhibit interfacial cracks, and enhance interfacial bonding
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Laser directed energy deposition (LDED) and laser strength. Demir et al. utilized the multi-material
powder bed fusion (LPBF), as two near-net shape LPBF system to fabricate 316L/Fe35Mn-graded multi-
manufacturing techniques, offer greater design freedom material parts with a tensile strength of 600 MPa. They
in fabricating graded multi-material parts, enabling the have discovered that due to the deliberate mixing of the
production of parts with more complex geometric shapes graded powder within the multi-material LPBF system and
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compared to traditional manufacturing methods. These sufficient melting of each layer, elements such as Cr, Ni, and
techniques have been applied in fabricating at least two Mo in the 316L were gradually replaced by Mn, resulting in
distinct metals in both vertical and horizontal directions a continuous-graded transition. Consequently, the method
within a part. LPBF utilizes a discrete-to-accumulative of graded joining in the fabrication of multi-material parts
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approach to fabricate solid parts. Based on a computer- could be expected to achieve good metallurgical bonding
generated 3D model, it employs a high-energy laser beam at the interface.
to selectively melt and solidify the pre-laid metal layer by Ti alloys possess high specific strength, excellent
layer to fabricate multi-material parts. With a smaller fatigue characteristics, and good high-temperature
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laser spot size and thinner layer thickness, LPBF enables behavior, while Al alloys exhibit good ductility and heat
the fabrication of more complex structures compared conduction alongside low density. 22,23 These properties
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to LDED. In laser additive manufacturing of multi- render them widely used in aerospace, automotive, and
material parts, the main challenge is the mismatching medical applications as lightweight and high-strength
of mechanical and thermal properties among different materials. The integration of both alloys in Ti/Al multi-
materials. During both the manufacturing and utilization material parts holds promise for significantly enhancing
processes, the unavoidable sharp interfaces can result the lightweighting efforts and overall performance of metal
in steep gradients in performance, which may become components. However, the distinct physical properties of
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focal points for residual stress concentration and lead Ti and Al alloys present challenges when combining them
to premature failure. In certain extreme cases, property for specific applications. During laser irradiation, as the
mismatches, such as thermal conductivity and melting molten pool approaches the melting point of Ti alloys,
temperature between materials, can render the forming Al alloys are susceptible to elemental depletion, resulting
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process entirely unsuccessful. At present, multi-material in gas entrapment and pore formation. In addition, the
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connections typically present three common joining formation of intermetallic compounds (IMCs) poses
methods. : direct joining, 13,14 graded path method, 15,16 and a major obstacle for Ti/Al multi-material systems. The
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intermediate section method. 17,18 Graded multi-material limited solubility between the two materials increases
parts can achieve a graded transition between two materials the likelihood of IMCs formation in Ti-Al system such
along the building direction, thus addressing the issue as Ti Al, TiAl, and TiAl during metallurgical reactions,
of mismatched interface performance in multi-material thereby resulting in decreased interfacial bonding strength
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systems. For example, 316L/CuSn10 multi-material parts of multi-material parts. 25
possess excellent electrical and thermal conductivity,
along with high specific strength and cost-effectiveness, Jing et al. investigated Ti6Al4V/AlSi12 multi-material
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making them widely applicable in industries such as parts prepared through LDED, resulting in a transition
power generation and heat transfer. However, the notable layer approximately 0.8 mm wide. They observed that the
difference in thermal expansion coefficients between presence of Si elements caused more complex metallurgical
Cu and Fe, as well as the high thermal conductivity of reactions at the interface and the uneven distribution of
Cu, results in an increased temperature gradient at the microhardness. Cracks were identified at the interface,

Volume 3 Issue 2 (2024) 2 doi: 10.36922/msam.3088