Achieving excellent strength and ductility via constructing high-density nanoprecipitate self-organized structure in an interstitial carbon alloyed multi-principal elements alloy

Abstract

The widespread adoption of multi-principal element alloys (MPEAs) is hindered by a strength–ductility trade-off: adding interstitial carbon increases strength but often triggers carbides at the grain boundaries (GBs) that severely degrade ductility. In this work, a novel strategy is proposed to overcome this dilemma by constructing the high-density nanoprecipitate self-organized structure (NSOS) within the grains. By introducing 0.2 wt% interstitial C and employing spark plasma sintering (SPS), an ultrafine dispersion of coherent L1₂-nanoprecipitates was spontaneously achieved during consolidation, without any post heat-treatment. This NSOS acts as an effective barrier to dislocation motion, blocking dislocation transmission to carbide and avoiding weakening of GBs. As a result, the alloy achieves an exceptional combination of strength and ductility: a yield strength of ∼1824 MPa and ultimate tensile strength of ∼1972 MPa with ∼7.6 % elongation, outperforming both the base alloy and lower/higher C variants. Mechanistically, the strength is elevated by dislocation and precipitation strengthening, while the NSOS enhances ductility through stress delocalization. The NSOS compels dislocations to expend their energy cutting through numerous nanoparticles instead of accumulating at GBs. This delayed and reduced stress localization at GBs carbides enables the activation of additional hardening mechanisms (stacking fault networks and deformation twinning), imparting high strain-hardening capacity. The findings showcase a new route to tailor MPEA microstructures via minor interstitial alloying and rapid sintering, yielding simultaneous high strength and ductility. This NSOS-mediated design strategy offers a promising pathway for developing advanced structural alloys with improved performance.