A comprehensive review of wire arc additive manufacturing for metallic functionally graded materials

Functionally graded materials are multifunctional materials, which consist of a spatial modification in composition and microstructure for the definite purpose of controlling variations in various functional properties like mechanical, thermal, and structural. They have been widely utilized in aerospace, healthcare, automobile, and various other industrial applications. Emerging additive manufacturing techniques such as wire arc additive manufacturing are capable of manufacturing complex shapes with gradual variations in composition, microstructure, and customized multifunctional material properties in an additive manner. Metal-based functionally graded materials have been extensively explored in recent times to achieve excellent properties, such as excellent strength and plasticity, good thermal stability, and notable anti-oxidation and anti-wear properties and thus additive manufacturing has proven one of the most necessary techniques to fabricate metal functionally graded materials. This paper intends to offer an in-depth survey of the current leading developments in wire arc additive manufacturing for metallic functionally graded materials and line up researchers, engineers, and industry professionals with an extensive understanding of the potentials, challenges, and opportunities related to wire arc additive manufacturing for functionally graded materials. Additionally, it explores the process parameters for optimizing and analysing various mechanical properties, microstructure, and corrosion behaviour of metal-based functionally graded materials. Early research into the potential of using wire arc additive manufacturing to create various alloys and metal combinations in diverse geometries showcases the many advantages of this emerging manufacturing technology, though further research is needed to justify its commercial application. Therefore, future research directions are proposed based on current findings and the challenges came across.