Thermo-kinetic origin for strength-ductility trade-off phenomena

Strength-ductility trade-off has been a long-standing dilemma in materials science, greatly limit the potential applications of various structural materials. Here, we explore the underlying physics of such paradox based on recently proposed generalized stability (GS) criterion. We propose that the strength-ductility trade-off relationship physically dominated by the correlation between thermodynamics driving force (ΔG) and the kinetic energy barrier (Q). Thus, we establish an intrinsic connection between GS criterion and mechanical properties, that high ΔG correspond to high strength, while small GS values associate with high plasticity. Additionally, we find that a new thermo-kinetic correlation ensuring sufficiently slow and steady dislocation slip in nano-twinned crystalline and gradient nanocrystalline, which break the original thermo-kinetic correlation for dislocation slip in nanocrystalline and achieve an excellent strength-ductility balance. This offers a quantitative method to optimize the strength and ductility of metal materials by thermo-kinetic properties.