Microstructural Evolution and Advanced Characterization of LPBF-Fabricated L605/IN718 Functionally Graded Superalloy

The increasing demand for high-performance multi-material components in aerospace, energy, and power generation industries necessitates advanced manufacturing techniques that overcome the limitations of traditional joining methods, such as welding and brazing. Additive Manufacturing (AM), particularly Laser Powder Bed Fusion (LPBF), offers a promising solution by enabling the layer-by-layer fabrication of complex multi-material structures and functionally graded materials without the need for filler materials. This research work focuses on the LPBF fabrication and fretting wear characterization of a novel L605/IN718 bi-material system, aiming to investigate its interfacial characteristics, microstructural evolution, and tribological behavior under severe conditions relevant to gas turbine applications.

Inconel 718 (IN718), a nickel-based superalloy, is widely recognized for its exceptional mechanical properties, including high stress tolerance and elevated temperature capability, making it critical for applications such as turbine engines. On the other hand, L605, a cobalt-based superalloy, is renowned for its outstanding wear and oxidation resistance, driven by solid solution and carbide strengthening mechanisms. The integration of these two materials promises synergistic properties essential for advanced component design, combining high strength and wear resistance.

The experimental methodology involved LPBF fabrication of L605/IN718 functionally graded rectangular bars using optimized parameters and a two-step heat treatment process to enhance microstructure and mechanical properties. Microstructural characterization revealed distinct material regions with a compositional gradient at the interface, promoting enhanced bond strength. Tribological testing demonstrated the superior wear resistance of L605, attributed to the formation of protective glaze layers, including Cr₂O₃ and spinel-like Co₃O₄. This research successfully demonstrates the LPBF fabrication of a high-quality L605/IN718 bi-material system with robust metallurgical bonding and tailored properties. The findings provide critical insights into the additive manufacturing of multi-material systems for demanding applications, enabling the design of components with enhanced performance in high-stress and high-temperature environments.