Trifunctional Laves precipitates enabling dual-hierarchical FeCrAl alloys ultra-strong and ductile

The synergy of ultra-high strength and large ductility is a vital requirement in particular for single-phase structural alloys; unfortunately these two properties are generally mutually exclusive. The hard-yet-deformable precipitates in alloys not only act as the strengthener that can block dislocation motion thus enhance the work hardening capability to strengthen materials, but also act as the stress buffer via self-deformation that releases local stress concentrations and as the cracking modulator that triggers multiple micromechanisms that resist crack propagation to ductilize materials. Here, taking the advanced FeCrAl-based alloy as an example, we confirmed a strategy that combines these triple functions of precipitates in a dual-hierarchical alloy by controllably embedding the multi-scaled hard-yet-deformable Laves precipitates in the lamellar coarse-grained matrix, where the lamellar boundary decorated by equiaxed ultra-fine grains serving as crack arresters. The proposed design concept of dual-hierarchically heterogeneous structure can achieve a substantial increase in yield strength up to the ultrahigh level ∼1.0 GPa by far with enhanced uniform elongation. These trifunctional Laves precipitates exhibit the interface-controlled mechanisms transited from dislocation cutting through coherent nanoscaled Laves precipitates to stacking fault-mediated plasticity of incoherent micro-scaled Laves precipitates. The present dual-hierarchical design strategy opens a new avenue to engineer materials with exceptional properties for superior fracture resistance.