Off-stoichiometry-guided design of high-strength chemically complex intermetallic-based alloys with outstanding ductility

•We demonstrate the feasibility of an off-stoichiometry strategy in designing ultra-strong and ductile chemically complex intermetallic alloys (CCIMAs).•A Co39.3Ni39.6Al13.8Ti3.1Ta2.8Nb1.4 (at.%) CCIMA with an ultrahigh tensile strength (-1.4 GPa) and a large tensile plasticity (∼30%) is successfully designed.•Such an ultrahigh strength is primarily ascribed to the high anti-phase boundary energy via multiple alloying additions (i.e., Ti, Ta, and Nb).•The nanoscale disordered phases at grain boundaries can efficiently enhance dislocation mobilities and plastic deformation compatibility, thus resulting in a large ductility.