The process of deformation twinning influences the flow behavior of FCC metals through two signature features ‚Äì plasticity accommodation via twinning shear and dynamic crystal refinement from the creation of twin boundaries. These dual features raise an interesting question: under which conditions do FCC metals nucleate or thicken deformation twins in response to plastic deformation? Nucleation-favored twinning causes a rapid segmentation of a microstructure, whereas thickening-favored twinning leads to a unit-step decrease in crystal size. In other words, a tendency towards nucleation-favored twinning creates obstacles in a microstructure that inhibit continued plastic flow and significantly influence work hardening behavior. In this talk, a first-principles criterion to evaluate the competition between nucleation and thickening of deformation twins in FCC materials is presented. This criterion is based on activation barriers retrieved from the generalized stacking fault energy landscapes of common FCC materials and is therefore free from phenomenological fitting. The development of this criterion is supported by kinetic Monte Carlo simulations and its predictive power is independently validated using molecular dynamics simulations of nanowires. This criterion provides new understanding of incipient twin formation and twin evolution pathways, which operate as a sub-branch under the traditional categories of deformation twinning and dislocation slip.

A First-Principles Criterion for the Evolution of Deformation Twinning in FCC Materials

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