Heterogeneous lattice strain strengthening in severely distorted crystalline solids.

Multi-principal element alloys (MPEAs) exhibit outstanding mechanical properties because the core effect of severe atomic lattice distortion is distinctly different from that of traditional alloys. However, at the mesoscopic scale the underlying physics for the abundant dislocation activities responsible for strength-ductility synergy has not been uncovered. While the Eshelby mean-field approaches become insufficient to tackle yielding and plasticity in severely distorted crystalline solids, here we develop a three-dimensional discrete dislocation dynamics simulation approach by taking into account the experimentally measured lattice strain field from a model FeCoCrNiMn MPEA to explore the heterogeneous strain-induced strengthening mechanisms. Our results reveal that the heterogeneous lattice strain causes unusual dislocation behaviors (i.e., multiple kinks/jogs and bidirectional cross slips), resulting in the strengthening mechanisms that underpin the strength-ductility synergy. The outcome of our research sheds important insights into the design of strong yet ductile distorted crystalline solids, such as high-entropy alloys and high-entropy ceramics.