Functionally graded materials (FGMs) replace the discrete interfaces of multi-material additive manufacturing with continuous compositional gradients, mitigating delamination and cracking, but reported systems for FGM direct ink writing (DIW) rely on specialized hardware that limits reproduction by other laboratories. This work presents the design, analysis, fabrication, and validation of a low-cost, modular active-mixing extrusion system for functionally graded DIW on a gantry platform. Two syringe pumps mounted on a stationary frame deliver feedstocks through flexible tubing to a gantry-mounted chamber, where a helical ribbon impeller and an extrusion screw on a single motor-driven shaft mix and deposit the material; all critical components are additively manufactured, including a transparent mixing chamber and a 316L stainless steel impeller. The system carries 0.464 kg on the gantry and uses 70 parts. Analytical calculations confirmed laminar delivery flow, Herschel–Bulkley computational fluid dynamics guided the extrusion screw geometry to a 0.01 mL/s target flow rate, and finite element analysis confirmed factors of safety of 11.8 and above 400 for the impeller and frame. Extrusion calibration showed a linear actuator-to-mass response within ±10%, and printing with two dyed kaolin clay slips produced visually smooth color gradients, demonstrating an accessible, reproducible platform for FGM-DIW research with clay-based feedstocks; validation with compositionally distinct ceramic and metal slurries and quantitative gradient characterization remain future work.

Multi-metal additive manufacturing (MM-AM) enables the fabrication of components with spatially tailored properties; however, achieving robust structural integrity at dissimilar metal interfaces remains a central technical challenge. This review critically examines interfacial design and processing strategies in MM-AM, with a particular focus on laser powder bed fusion (L-PBF) and laser directed energy deposition (L-DED). An operational diagram is introduced to systematically categorize the key factors governing metallurgical bonding in MM, including thermal expansion mismatch, phase incompatibility, and solidification behavior. Using this diagram, the review synthesizes current understanding of interfacial integrity mechanisms in bi-metallic systems. Process-driven mitigation strategies are then evaluated and classified into two primary approaches: the use of compositionally compatible interlayers and hybrid additive manufacturing (H-AM) strategies incorporating additional thermal, mechanical, or thermo-mechanical treatments during MM-AM. These approaches are critically assessed for their effectiveness in suppressing defect formation, including brittle intermetallic compounds and the accumulation of residual stress. Finally, an engineering-oriented framework is proposed to guide material selection and process design, providing a foundation for the scalable fabrication of structurally integrated multi-metal components.

Three dimensional freeze printing (3DFP) combines the advantages of freeze casting and additive manufacturing to fabricate multifunctional aerogels. Freeze casting is a cost-effective, efficient, and versatile method capable of fabricating micro-scale porous structures inside the aerogels for many different applications. The 3DFP provided the capability of fabricating highly customized geometries with controlled microporous structures as well. However, there are still many unexplained phenomena and features because of the complexity of post-processes and indirect observation methods. This study demonstrates the design and construction of the in situ imaging systems, which use the x-ray synchrotron radiography to observe freeze casting and 3DFP processes. With the advantages provided by the in situ x-ray imaging techniques, the ice crystal growth with its unique lamellar structures can be observed during the freeze casting process. The movement of freeze front, material deposition, and growth of ice crystals can also be visualized during the inkjet-based 3DFP process.