| Mechanisms for generation of nanoscale twins at free surfaces in nanomaterials during their plastic deformation are theoretically described. The three mechanisms are examined which represent (i) successive events of partial dislocation generation at free surfaces and their further glide in adjacent grain; (ii) cooperative generation of partial dislocations at free surfaces and their further cooperative glide in adjacent grain; and (iii) nanoscale multiplane shear initiated at free surfaces. The energy and stress characteristics of the nanoscale twin formation through these mechanisms in nanocrystalline copper (Cu) are calculated. Competition between the twin generation mechanisms in nanomaterials is discussed in the exemplary case of copper. |
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