Enhanced ductility via high-density nanoprecipitates driven by chemical supersaturation in a flash-heated precipitation-strengthened high-entropy alloy

Precipitation strengthening is an effective method to strengthen high-entropy alloys (HEAs); however, the incompatible plastic deformation caused by precipitates accelerates the initiation and development of cracks, reducing ductility. Therefore, it is necessary to spare no effort to overcome this strength–ductility trade-off. However, improving the ductility of HEAs without losing the precipitation-strengthening effect remains a daunting challenge. The strategy of this study is to increase chemical supersaturation without introducing other defects to drive the formation of high-density nanoprecipitates to share stress, reduce localization, and alleviate incompatible plastic deformation, thereby fully utilizing the strain-hardening ability to improve the ductility of HEAs without reducing their strength. Specifically, common Ni ₃₅(CoCrFe) ₅₅Al _5.5Ti _4.5 (at.%) precipitation-strengthened HEAs were selected as the experimental object. Short-term high-temperature flash heating causes the dissolution of the initial nanoprecipitates, and the separated atoms form chemically supersaturated microregions in the matrix between the initial nanoprecipitates after insufficient short-range diffusion, resulting in the formation of high-density new nanoprecipitates. The density of the nanoprecipitates reaches 5.0 × 10 ²⁴ m ⁻³, representing a two-order increase in magnitude compared to the aging state (1.9 × 10 ²² m ⁻³). By increasing the density of nanoprecipitates, multiple nanoprecipitates share stress together. Sufficient slippage of dislocations maximizes the potential excellent strain-hardening ability, considerably improving the ductility of HEAs. Moreover, the strategy of improving the ductility by increasing the density of nanoprecipitates can be applied to many other precipitation-strengthened alloy systems.