Additive manufacturing of metal-based functionally graded materials: overview, recent advancements and challenges

Additive Manufacturing (AM) techniques gained significant research interest in the past two decades. AM techniques are the best alternative to traditional manufacturing processes for fabricating highly complex parts with reduced wastage. Functionally graded materials (FGMs) are heterogeneous structures with varying composition, microstructure, and site-specific properties, which is beneficial in a wide variety of applications. Manufacturing constraints in FGM by conventional manufacturing methods limit the applications. Significant advancements in AM methods form the bedrock to manufacture complex FGM structures. Applications of FGM drastically increased due to the feasibility of AM processes. The number of research publications in FGM depicts the interest in the research trend. AM was widely used to fabricate a variety of FGM's, but certain defects developed in the FGM components due to the significant variance of thermal properties, crystallographic structures, and modulus of elasticity require focused and systematic investigation. The AM process progresses drastically to control the defects by hybrid process, using artificial intelligence (AI) controlled design and process. In the present review, various studies focused on the fabrication of FGM with stainless steels, magnesium, titanium, copper, and nickel-based superalloys have been discussed. This article reveals the important knowledge required for fabricating quality metal-based FGM structures using AM technology and its benefits in identifying future trends and challenges. Ultimately, the outlook is summarized to give direction for future research works.