Crack-Free Tungsten Fabricated via Laser Powder Bed Fusion Additive Manufacturing

Additive manufacturing of tungsten (W) is challenging due to its high melting point, high thermal conductivity, oxidation tendency, and brittleness from grain boundary (GB) oxides. In this study, the processing of W through laser powder bed fusion is investigated. Parts are fabricated under argon (Ar) and nitrogen (N₂) atmospheres using the same processing parameters. The part produced in Ar has cracks with oxide precipitates decorating the fractured GBs. On the other hand, crack-free W samples are produced under N₂ atmosphere without any additional process modification. In both cases, the oxygen (O) content in the LPBF samples is similar to the starting powder. Interestingly, the analysis of the samples fabricated in nitrogen suggests that nitrogen is retained beyond the equilibrium solid solubility limit, while high-resolution electron micrographs of fractured surfaces reveal reduced levels of oxides at GBs. Increased hardness for samples processed under N₂ atmosphere is observed. Density Functional Theory (DFT) calculations performed to study the influence of interstitial nitrogen on oxygen diffusion in W indicated a hindrance to O diffusion from the presence of dissolved N.