Tuning the microstructure and strengthening mechanism of the CoCrFeNi high-entropy alloy via doping metalloid and interstitial elements

Abstract

The synergistic strengthening and toughening of metalloid and interstitial elements were demonstrated for the first time in the CoCrFeNi high-entropy alloy (HEA) by the sequential addition of Si, B, and N elements. The addition of Si simultaneously enhances the strength and ductility of the CoCrFeNi HEA, further, the doping of B promotes the formation of Cr2B precipitates and the grain refinement, and the addition of N further refines the grain size and increases the lattice distortion and the degree of chemical short-range order (SRO). The strengthening effect to yield strength of the addition of Si, B, and N elements is well described by the strengthening model. Doping Si, B, and N elements can regulate the stacking fault energy (SFE), lattice distortion, and short-range order of the alloy, and consequently induce the multiple twins and nanoscale transformation from the face-centered cubic (FCC) to the hexagonal close-packed (HCP) phase upon room-temperature tension, which enhances the work-hardening capability of the alloy. Finally, a dual heterostructure of grain size and precipitate phase distribution is formed in CCFN-Si-B-N-700 HEA by regulating heat treatment. The yield strength of the current alloy is further enhanced up to 1.2 GPa, and the ductility is maintained at 13 %. This study not only provides new insights into the strengthening and toughening mechanism of metalloid and interstitial elements but also a new paradigm for the development of HEAs with excellent strength-ductility synergy.