Cobalt-Free High-Entropy Alloys with Enhanced Strength–Ductility Synergy and Reduced Thermal Diffusivity

Abstract

Developing advanced thermal barrier interlayers remains highly challenging due to the stringent requirements of simultaneously achieving high mechanical strength, sufficient ductility, and low thermal diffusivity. To address these limitations, a low-cost cobalt-free V10Cr15Fe30Mn15Ni30 HEA was designed. The alloy was cold-rolled to 80% thickness reduction. It was then annealed at 823–1223 K for 30 min. The annealed samples showed excellent strength–ductility synergy. They delivered an ultimate tensile strength over 1 GPa. The total elongation reached 15%. All annealed samples had low thermal diffusivity. Quantitative analysis revealed the strengthening mechanisms. Grain boundary strengthening and dislocation strengthening dominated yield strength increases below 1023 K. Grain boundary strengthening prevailed at and above 1123 K. This work offers new insights into how to leverage σ-phase precipitation for mechanical enhancement. It also tailors reduced thermal diffusivity through precipitate–matrix interface modifications. Refined grains, moderate dislocation density, σ-phase scattering, and severe lattice distortion work together. These effects increase the structural robustness and thermal barrier functionality of cobalt-free HEAs.