Laser powder bed fusion of Mo and W in nitrogen environment

The additive manufacturing of Group VI BCC elements such as molybdenum (Mo) and tungsten (W) is challenging due to their high melting point, oxidation tendency, and grain boundary (GB) oxide brittleness. This presentation will compare the processing of Mo and W by laser powder bed fusion (LPBF) in argon and nitrogen environments. LPBF of both elements produced in argon resulted in samples with grain boundary cracks decorated with oxide precipitates, while the samples processed in nitrogen were crack free and with reduced oxide precipitate content. In both cases supersaturated levels of N were observed. Density functional theory calculations were used to explain the supersaturated nitrogen content and its influence on oxygen diffusion.