Processing-Microstructure Investigation of Nb-V-Zr and the Role of Compositional Segregation on Mechanical Behavior

Refractory high entropy alloys (RHEAs) have gained considerable attention for their potential as the next generation of high-temperature materials due to their unique design strategies and excellent mechanical properties. While tremendous progress has been made in this field, there is still a lack of knowledge on the effects of processing and composition on the microstructural development of these alloys. In this work, we apply a high-throughput synthesis technique to investigate the processing-composition-structure relationships in Nb-V-Zr. This medium entropy alloy is chosen as a model system as it forms the basis for many RHEAs that have been studied to date. We use direct laser deposition to rapidly synthesize microstructural libraries under a wide range of heating and cooling rates, as well as compositional libraries with varying Nb and Zr concentrations. BCC dendrites are observed, separated by two Laves phases, cubic C15 and hexagonal C14. Phase size, spacing, and morphology are correlated with laser power, travel speed, and composition. Compositional segregation is also observed in the microstructure, where the dendrites have a Nb-enriched center and Zr-enriched edges, while the interdendritic region is enriched in V. Transmission electron microscopy is used to investigate the coherency between these interfaces. Nanoindentation experiments are performed to investigate the role of compositional segregation on mechanical properties.