Selective laser melting additive manufacturing of tungsten with niobium alloying: Microstructure and suppression mechanism of microcracks

Highlights: • High dense W-5Nb samples with few microcracks were obtained by selective laser melting technique. • The distribution density and segregation extent of nanopores formed by W_xO_y vaporization were reduced. • Solid solution strengthening existed in W with Nb alloying. • The microcrack suppression was attributed to solid solution strengthening and distribution discretization of nanopores. -- Abstract: Microcrack suppression is a challenging issue in additive manufacturing of tungsten heavy alloys (WHAs) due to the high melting point and brittleness of tungsten (W). In this study, W-5Nb samples with a high density and few defects were successfully manufactured by introducing niobium (Nb) using selective laser melting (SLM) technique, and the influence of process parameters on the density and microstructure of W-5Nb was investigated. The effect of Nb addition on the mechanism of the microcrack formation was mainly analyzed. The results revealed that the densification first increased and then decreased with the increase of energy density (E). When E was 397 J/mm³, samples with the relative density of 98% and W-Nb solid solution phase were obtained, and the microcracks were basically suppressed. The distribution segregation extent and density of nanopores formed by W_xO_y gasification were reduced, which was beneficial for improvement of grain bonding strength. Solid solution strengthening occurred in W with Nb alloying and also contributed to improvement of grain bonding strength. The percentage of the large-angle grain boundaries (>15°) was reduced by 67% (12.9% for E = 397 J/mm³ and 39.6% for E = 556 J/mm³) due to uniform grain deformation with grain bonding strength being enhanced.