Ultrafine CoCrCuFeNi high entropy alloy thin films with high strength, plastic deformability and thermal stability achieved via grain engineering and nanoclustering

Abstract

The design of high-performance structural materials is always pursuing the combination of mutually exclusive properties such as mechanical strength, plasticity and thermal stability. Although high entropy alloys thin films (HEAs-TF) show promising mechanical and thermal properties, the development of novel nanostructures with unique nanoscale features is needed to overcome the strength-plasticity-thermal stability trade-off, going beyond a conventional compositional control. Here, we present a new synthesis route to fabricate ultra-strong, highly plastic, and thermally stable HEAs-TF leveraging the unique capabilities of pulsed laser deposition (PLD). We demonstrate our approach by focusing on CoCrCuFeNi, a model FCC HEA of the original Cantor family. Specifically, we synthetize ultrafine grain structures with controllable size (down to 12 nm) which can be further tailored by post-thermal annealing treatments, resulting in high hardness (11 GPa) and yield strength (2.0 GPa) due to Hall-Petch strengthening, outperforming similar HEAs-TF while maintaining high plasticity (no fracture at 30% strain). Moreover, these ultrafine HEAs-TF shows enhanced thermal stability, grain growth starting at T = 49% of T_m (melting temperature), while maintaining high hardness (9.1 GPa) after annealing for 1 h at 460°C. The PLD-deposited ultrafine HEAs-TF lead to mutual thermodynamic and mechanical stabilization, opening up a new approach for stable, strong and ductile materials.