PNNL

Abstract

Thin-film deposition is being proposed as a primary method to rapidly screen new compositions for high-throughput alloy design, but its effectiveness in predicting bulk alloy behavior remains uncertain. This study compares the microstructure and mechanical properties of thin-film and bulk refractory high-entropy alloys (RHEAs) to evaluate the reliability of thin-film-based screening. A five element, NbMoTaTiV RHEA was selected, with elemental variations generating 15 thin-film alloys, of which five were synthesized via arc melting for bulk property comparison. Phase analysis confirmed that both thin films and bulk alloys exhibit a single-phase BCC structure, suggesting that thin films can successfully help predict phase formation. However, elemental distribution analysis revealed no chemical segregation in thin films, whereas bulk alloys exhibited composition-dependent segregation patterns that remained stable even after 24 hours of heat treatment at 1200°C, highlighting challenges in homogenization. While nano-hardness trends in thin films aligned with bulk Vickers hardness, discrepancies were observed in certain compositions. Moreover, quasi-static compression testing showed that hardness alone is not a reliable predictor of yield strength (YS). Specifically, a composition, which exhibited the highest hardness, had the lowest YS and ductility. These findings demonstrate that thin-film screening alone cannot fully capture bulk mechanical performance due to the influence of segregation and microstructural inhomogeneities. While thin films provide a useful initial assessment of phase stability and hardness trends, bulk-scale validation remains essential for selecting alloys for structural applications.