Achieving synergy of strength and ductility of eutectic high-entropy alloys via continuous precipitation of nano-precipitates

Abstract

This study examines the impact of solid solution aging treatment on the microstructure and mechanical properties of carbon interstitial solution AlCoCrFeNi_2.1 eutectic high-entropy alloys (EHEAs). The results show that after solution treatment, carbon atoms are fully dissolved in the matrix. In carbon-free alloys, the body-centered cubic (BCC) phase adopts a rod-like structure, whereas carbon-doped alloys exhibit a spherical morphology. After aging at 500 °C, a small amount of precipitate appears along the phase boundary. At 600 °C, disk precipitates continuously precipitate along the phase boundary. However, at 700 °C, the disk nano-precipitates transform into coarser particles and short rod-like structures that are unevenly distributed within the BCC phase and at the phase boundaries. Mechanical testing reveals that after solution treatment at 1300 °C for 6 h and aging at 600 °C for 4 h, the alloy achieves a yield strength of 566 MPa, tensile strength of 1043 MPa, and elongation of 11.3 %, reflecting a favorable balance of strength and ductility. Strengthening is attributed to nanoscale precipitates at phase boundaries, which create significant dislocation barriers. These nano-precipitates bond strongly with the matrix, enabling coordinated dislocation movement and promoting plastic co-deformation of both phases, thereby maintaining alloy plasticity.