Exceptional strength-ductility synergy in a casting multi-principal element alloy with a hierarchically heterogeneous structure

Designing multiscale heterostructures by taking lessons from Nature provides a promising strategy for achieving excellent strength-ductility synergy in metals and alloys. The achievement of this goal usually requires intricate multi-step thermomechanical processing, but this is still a challenge with casting alloys rather than wrought ones. Here, we developed a Cr30Fe30Ni30Al5Ti5 (at.%) casting multi-principal element alloy (MPEA) which exhibits, in the as-cast condition, a hierarchically heterogeneous structure involving precipitates at multiple length scales. Microscale body-centered-cubic (BCC) grains are dispersed throughout a continuous face-centered-cubic (FCC) structural framework. Coherent L12 nanoparticles form in the FCC matrix, while abundant nanoparticles with hierarchical dimensions (i.e., of η, B2, and η/L21 phases) precipitate inside the BCC grains. The synergistic interactions between dislocations and multiscale precipitates which induce massive dislocation networks and stacking faults result in stable strain-hardening behavior, endowing the alloy with an exceptional combination of strength and ductility without the need for homogenization and complex processing. We believe that this represents a breakthrough that surpasses known casting MPEAs and offers implications for developing new high-performance casting alloys.