W-Ta alloys processed by Laser-Based Powder Bed Fusion: how microstructure and properties change with Ta concentration

In this paper, a study of 4 tungsten-tantalum binary alloys processed by Laser-Based Powder Bed Fusion (PBF-LB) is presented. The evolution of the microstructure and the properties of the material in dependence on the tenor of tantalum inside the alloy was investigated, selecting 0wt.%, 2.5wt.%, 7.5wt.%, and 15wt.% as the Ta concentrations. The optimal process window for each examined alloy was investigated. The introduction of tantalum in the alloy was effective in mitigating the cracks in the tungsten matrix. However, the energy provided to the material in the additive manufacturing process was also determinant for achieving an almost crack-free and low-porosity material. Moreover, the range of concentrations of Ta considered in this work allowed the authors to see that the properties of the binary alloys examined don’t lead to a continuous improvement with the addition of Ta, but start decreasing for Ta contents higher than 7.5wt.%. The minimum porosity volume fraction achieved in this study was 0.7 % for the W-7.5wt.%Ta blend. The same alloy showed the highest hardness among the other materials investigated, reaching hardness values above 480 HV0.5, approximately 30 % higher than what was obtained for pure tungsten, and with a 50 % increase in the ultimate compressive strength compared to the unalloyed material. XRD analyses confirmed that the tantalum particles solubilize completely inside the tungsten matrix, assuring a good homogeneity of the composition and the absence of segregations and secondary phases inside the additively manufactured parts.