Achieving high strength and ductility in nitrogen-doped refractory high-entropy alloys

•A combination of high strength and ductility in TiZrNbTa HEAs was achieved by doping nitrogen.•Interstitial strengthening contributes to the enhanced strength. The improved ductility originates from the promoted planar dislocation slip inside grains.•Annealing further increases the strength and ductility of the nitrogen-doped TiZrNbTa HEA.•The improved strength and ductility in the annealed HEAs attributes to the nitrogen solid solution strengthening, in situ grain refinement and promoted dislocation cross slip.