Enhancing intrinsic ductility in VNbMoTaW high entropy alloy: A combinatorial investigation with experimental evaluation of theoretical predictions

The application of refractory high entropy alloys (RHEAs) as engineering materials has been hindered by their poor inherent ductility. In this study, a novel approach combining thin film combinatorial screening with fragmentation testing was employed to identify intrinsically ductile alloy compositions. Inspired by the physics-based intrinsic ductility parameter, the ‘χ-parameter,’ we investigated the replacement of group VI elements (W/Mo) with group V elements (V, Nb, Ta) in the VNbMoTaW system. Conventional combinatorial analyses, including composition, phase, and hardness assessments, were conducted across a wide range of non-equiatomic configurations. The results revealed a broad compositional space favoring a single-phase body-centered cubic (BCC) solid solution with comparable hardness, despite significant differences in element concentrations. Thin film fragmentation testing was then performed on VNbMoTaW, VNb₂TaW, VNbMoTa₂, V₂NbTaW, and V₂NbMoTa systems, establishing a ductility trend based on crack onset strain (COS) and residual stress. To further validate the thin film findings, indentation fractography was performed on bulk samples. The replacement of Mo with Nb emerged as the most effective strategy for enhancing ductility in both experiments. Finally, experimental results were compared against five theoretical approaches.