Review on laser powder-based directed energy deposition for fabricating functionally graded materials: Microstructure, mechanical behavior, and defect analysis

Additive manufacturing (AM) has emerged as a transformative technology, enabling the fabrication of complex geometries through a layer-by-layer approach. This advancement aligns with the goals of Industry 4.0, offering substantial benefits for large-scale sectors such as aerospace and automotive. Notably, AM not only facilitates the production of intricate parts but also enables efficient and cost-effective repair solutions. This review examines the novel application of laser powder-directed energy deposition (LP-DED) in fabricating functionally graded materials (FGMs). These are engineered to exhibit a gradual change in composition and properties across their volume. The study highlights how LP-DED offers precise control over processing parameters, such as laser power, scan speed, and powder feed rate, to tailor material characteristics such as hardness, thermal resistance, and corrosion behavior. A key novelty of this work lies in its focus on dynamically altering powder composition during deposition to achieve customized gradients in material performance. Furthermore, the paper synthesizes findings from the recent literature, analyzing the microstructural evolution, defect formation, and mechanical behavior of LP-DED-processed FGMs. By addressing both the opportunities and challenges of this advanced method. The review provides actionable insights for selecting optimal materials and process settings, emphasizing the growing role of LP-DED in next-generation manufacturing strategies.