In situ gradient nanoprecipitation enables alloys with record-high as-cast strength−ductility synergy

Abstract Direct manufacturing of alloys through casting is economical, user-friendly, and conducive to near-net-shape processing, and therefore of great application interest. However, as-cast alloys are rarely used directly, because without post-cast thermomechanical treatments, the solidification product is susceptible to coarse grains, compositional segregation, and particularly unsatisfying precipitates, which tend towards inadequate strength and brittleness. These ubiquitous disadvantages have long and seriously hindered practical applications. Here, through screening using thermodynamic calculations and calorimetric monitoring, we successfully landed non-equiatomic NiCoCrAlTaZrB complex-concentrated alloys (CCAs) to realize in situ, micro-segregation-induced size-gradient L12 nanoprecipitates increasing from dendritic to interdendritic regions. Consequently, without any post-cast treatment, prolific in situ nanoprecipitation strengthening renders ultrahigh as-cast yield strength at gigapascal (GPa) level, while multi-scale chemical/structural segregation heterogeneities reinforced by gradient nano-precipitates result in progressive and persistent hetero-deformation within dendrites, thereby sustaining high strain-hardening rate of ~3 GPa and uniform tensile elongation up to ~32%. Such robust as-cast strength−ductility synergy not only exceeds all previous as-cast CCAs, but also outperforms all commercial alloys that have already been optimized via post-cast treatments. This advance through exploiting in situ size-gradient nanoprecipitation accomplishes a goal more practical than the common pursuit for property records, which all require downstream (multi-step and/or subtractive) processing that increases production time, expenses, and even severe environmental concerns.