Additive manufacturing of functionally graded materials: Advances, challenges, and strategies for processing and performance optimization

Functionally Graded Materials (FGMs) represent a significant advancement in material science, offering the possibility of tailoring properties in components by gradual transitions in composition, porosity and microstructure. These materials provide solutions for thermal, mechanical, and wear-related challenges in aerospace, biomedical, nuclear, and energy industries. While significant progress has been made in understanding and manufacturing FGM, fundamental challenges remain in optimizing their fabrication, performance, and industrial scalability. Regarding the fabrication of FGMs, various conventional methods have been used. However, there are several intrinsic shortcomings in these methods that hinder the fabrication of FGM with the desired microstructure and properties, which are overcome by the introduction of Additive Manufacturing (AM) techniques. Thus, AM has opened new pathways for precisely engineering FGM, enabling controlled, gradual transitions between different material phases. However, despite these advancements, key challenges remain, including interfacial defects, residual stress management, process optimization, and long-term stability of FGM in real-world applications. Given AM technologies' rapid development and growing impact on FGM research, this work will provide a review including the conventional techniques and AM-techniques for the manufacturing of FGM. This review will focus on the latest advancements in the development of FGM with respect to manufacturing and materials systems, the remaining challenges, and future research directions. This review aims to bridge the gap between research and industrial applications by addressing these aspects, guiding future developments in next-generation FGM.