Laser powder bed fusion of pure Nb and Nb + WC powder mixture

Abstract

Additive Manufacturing (AM) of high temperature refractory metals, including Nb-based alloys, can overcome the challenges associated with their processing using the conventional methods. In this study, pure Nb and a blend of Nb with 2.5 wt% WC was processed with Laser Powder Bed Fusion (LPBF) starting with a full optimisation cycle that explored the impact of the laser power, scan speed, hatch spacing, and layer thickness on the build integrity. Results show that both materials have good processability, as confirmed by the lack of cracking and other defects once the parameters are optimised. Nevertheless, the process parameters affected the materials in different ways. Increasing both the scan speed and laser power resulted in hardness increase in pure Nb. However, this was not seen in the case of the Nb + 2.5 wt% WC powder mixture. In fact, the hardness was on average ∼ 15% lower in the Nb + WC builds compared with pure Nb builds. This observation was elucidated through studying the effect of the process on the oxygen pick-up in pure Nb and the dissociation of the carbide in the Nb + WC mixture. Although the hardening effect is expected due to the full solubility of W in Nb or due to the formation of carbides, results indicate that oxygen pick-up has a greater impact on hardness.