Mitigating the challenges in additive manufacturing of refractory complex concentrated alloys using Ti alloying via multi-material feedstock approach

The development of novel refractory complex concentrated alloy material systems for extreme environments, despite the promise, is hindered by significant processing challenges during fabrication. These challenges primarily stem from their intrinsic properties: high hardness and brittle nature restrict deposition through impact-based approaches such as cold spray additive manufacturing (CSAM), while the wide variation in melting temperatures among constituent elements limits the processability by melting and solidification - based additive manufacturing techniques such as laser-based powder bed fusion (LB-PBF). In this study, a composite feedstock approach was employed to mitigate the aforementioned-challenges during CSAM and LB-PBF processing. Commercially pure Ti was employed as the secondary material and was mixed with a custom-developed TaNbTiVCr alloy at varying volumetric ratios. The CSAM and LB-PBF printed specimens were systematically characterized in terms of their microstructure and microhardness. CSAM and LB-PBF printed specimens with different volume fractions of mixing demonstrated excellent build quality, with negligible porosity and crack formations, albeit with inhomogeneous microstructures. In the case of CSAM, the specimen with highest TaNbTiVCr content retained comparable hardness to that of the feedstock powder, despite Ti addition. The Ti particles offered a cushioning effect to the impacting TaNbTiVCr particles, thereby limiting the inter-particle interaction between them, aiding the deposit build-up. On the other hand, Ti addition for the LB-PBF processing played a critical role in inhibiting the formation of hot-cracks and lack-of-fusion porosities. However, this was at an expense of lower hardness compared to the CSAM counterparts. Overall, this systematic study highlights the potential of employing a composite feedstock approach to significantly enhance the processability of the complex refractory alloys through additive manufacturing.