Characterization of microstructure and mechanical properties of L-DED processed Ni-Al alloy with different Ni/Al ratios for design of Ni-Al functionally graded materials

Ni-Al bimetallic structures, which combine the excellent high-temperature mechanical properties of Ni-based alloys and the light-weight of Al-based alloys, exhibit significant potential for applications in aerospace, automotive, and defense-related industries. However, differences in the coefficients of thermal expansion and the formation of intermetallic phases between the two alloys impair stable interfacial bonding and structural integrity. While welding and cladding processes have been extensively applied to address these issues, their applicability is limited when fabricating intricate geometries. To overcome these challenges, the laser-directed energy deposition (L-DED) process was introduced. This technique enables the simultaneous deposition of different metal powders at specified ratios, allowing for the fabrication of functionally graded materials (FGMs) with gradually varying mixing ratios. In this study, this capability of L-DED was utilized with ultimate goal of fabricating Ni-Al FGM structures. Understanding the microstructure and mechanical properties of L-DED samples at each specific powder mixing ratio is essential for optimizing the graded design of FGMs. Accordingly, Inconel 625 and Al-10Si-1Mg powders were deposited at various mass ratios, and appropriate process parameters like laser power, scanning speed and dwell time were selected considering thermal stability. The resulting microstructures and mechanical properties were analyzed to establish foundational data for the optimized design of Ni-Al FGM structures.