Computational design and experimental verification of Ta-Ni-Co metallic glasses produced via gas atomization

Metallic glasses (MGs) have many beneficial properties for use as structural materials and coatings in extreme environments. However, typical MGs face major challenges for high-temperature applications, as MGs with high glass forming ability (GFA) are often encountered in low melting temperature systems. Refractory metal-based MGs have been explored to push the usefulness of MGs to higher temperatures. Due to relatively low GFA, the part thickness that could be achieved in these alloys is typically limited. To overcome this challenge, additive manufacturing (AM) has been used to produce bulk glassy parts and coatings from powder feedstock. In this study, refractory Ta-Ni-Co glassy powders were successfully synthesized via gas atomization. Two models were used to predict GFA: an empirical parameter (P_HSS) and the atomic cluster-plus-glue-atom (CPGA) model. Both models predicted similar composition regions with the highest GFA, which were near a ternary eutectic and in the vicinity of the topologically close-packed (Ni,Co)Ta intermetallic referred to as the μ phase. Powders with the least amount of crystallinity were within the highest GFA region. One fully amorphous powder was produced (Ta_37.4Ni_39.9Co_22.7) from a composition closest to the eutectic. Deformation mechanisms and mechanical properties measured through nanoindentation were found to change substantially upon devitrification of the amorphous powder, indicating a strong dependence on crystallinity. As precipitation of the µ intermetallic was found to increase both hardness and reduced modulus, partially crystalline Ta-Ni-Co MG powder may be a suitable feedstock for additive manufacturing of matrix composites for extreme environment applications.