Metallic multi-material structures are heterogeneous structures characterized by changing composition, microstructures, and site-specific characteristics, advantageous for numerous applications where multifunctionality is desired. Metallic multi-material structures are known as bimetallic structures (BSs), which are functionally graded materials (FGMs). In recent years, wire-arc additive manufacturing (WAAM) advanced as a promising additive manufacturing process to realize the fabrication of these structures due to its high deposition rate, cost-effectiveness, and material utilization efficiency. This review presents a comprehensive overview of the recent progress, processing strategies, and scientific challenges in WAAM of multi-material structures. The paper begins with an introduction to multi-material structures, followed by a bibliometric analysis of the current research landscape. Conventional and additive manufacturing fabrication approaches are presented. The review highlights key developments in processing strategies and critically evaluates research studies on WAAM of BS and FGMs. Major scientific challenges, including porosity, lack of fusion, residual stresses, cracking, material compatibility, and brittle intermetallic phase formation, are critically analyzed. Additionally, modeling, simulation, and process automation issues are discussed as barriers to industrial-scale implementation. The paper concludes with an outlook on future research directions to address existing challenges and accelerate the adoption of WAAM for complex multi-material components.

Metallic multi-material structures are heterogeneous structures characterized by changing composition, micro-structure, and site-specific characteristics, advantageous for numerous applications where multifunctionality is desired. Metallic multi-material structures are known as bimetallic structures (BS), functionally graded materials (FGMs). In recent years, Wire Arc Additive Manufacturing (WAAM) advanced as a promising additive manufacturing process to realize the fabrication of these structures due to its high deposition rate, cost-effectiveness, and material utilization efficiency. This review presents a comprehensive overview of the recent progress, processing strategies, and scientific challenges in WAAM of multi-material structures. The paper begins with an introduction to multi-material structures, followed by a bibliometric analysis of the current research landscape. Conventional and additive manufacturing fabrication approaches are presented. The review highlights key developments in processing strategies and critically evaluates research studies on WAAM of BS and FGMs. Major scientific challenges, including porosity, lack of fusion, residual stresses, cracking, mate-rial compatibility, and brittle intermetallic phase formation, are critically analyzed. Additionally, modeling, simulation, and process automation issues are discussed as barriers to industrial-scale implementation. The paper concludes with an out-look on future research directions to address existing challenges and accelerate the adoption of WAAM for complex multi-material components.

In this study, the fused deposition modelling (FDM) process is utilized to develop the short glass fiber (SGF) reinforced 3D printed Acrylonitrile Butadiene Styrene (ABS) polymer composites. Three filaments for FDM were prepared by varying SGF reinforcement percentages in ABS matrix 0%, 15%, and 30% respectively. The microstructural analysis of SGF reinforced ABS filament was carried out to understand bonding and dispersion. The composites were analyzed for their microstructure, mechanical properties and fracture behavior. Short glass fibers were uniformly distributed in composite ABS matrix, with strong interfacial bonding between ABS and SGF, and no clustering or gaps at interfaces. Tensile test demonstrated that the ultimate tensile strength (UTS) was significantly enhanced with SGF inclusion, peaking at 49.7 MPa for the ABS/30%SGF composite, demonstrating the strength advantages of fiber reinforcing. On the contrary, the presence of SGF negatively affected material elongation, with the ABS/30%SGF composite showing the least flexibility, likely due to restricted polymer chain mobility. Fractured tensile specimens revealed a transition from ductile fracture in neat ABS to brittle fracture in SGF composites, with the latter lacking plastic deformation features. The ABS/30%SGF composite had the highest flexural strength, demonstrating enhanced fiber-matrix bonding and fiber distribution, resulting in a 58.2% and 12.7% increase in strength compared to neat ABS and the ABS/15%SGF composites, respectively.