Functionally Graded Structures via LPBF: Interfacial Bonding and Corrosion Performance

Designing materials for high-temperature and oxidation-resistant environments with balanced properties remains a significant challenge with competing requirements between service conditions and environment-material interfaces. Single-material systems frequently fall short, but functionally graded materials (FGM) provide a solution via localized composition control. Complex FGM structures can be fabricated using laser powder bed fusion (LPBF) with the help of a custom-made in-situ powder deposition system. In LPBF of FGM, residual stress and defects, particularly in refractory metals such as tungsten (W), persist due to rapid thermal cycles. This study demonstrates how the fabrication of multi-powder layers of tungsten and nickel alloys (bimetallic FGM structure) with varying laser power affects the interfacial bonding, residual stress, and hardness. This study elaborates on how these changes are related to energy density. More pertinent to the application of W and IN718 under harsh environments, the corrosion resistance of W-IN718 FGM was also studied using electrochemical impedance spectrometry (EIS), and the results were compared to those of tungsten heavy alloy (WHA) and to each of the base materials (W and IN718). The results showed good bonding achieved through solid-state diffusion with improved material properties of hardness and successful fabrication of pure W powder with less residual stress and defects usually faced, such as cracks and pores at the interlayers. The FGM structure fabricated using LPBF proved to achieve an improved corrosion performance beyond WHA and pure W. The results of this study point to a promising direction of combining W and IN718 as FGM via LPBF.