Non-twinning deformation mechanism of pure copper under high speed electromagnetic forming

• Non-twinning deformation mechanism of pure Cu under electromagnetic forming was observed.
• Twin boundaries in Cu decrease with increasing plastic strain during EMF process.
• The mechanism is understood deeply on the basis of the nucleation of partial and perfect dislocations.

The conventional high strain rate forming usually induces the occurrence of deformation twins in face-centered-cubic metals such as copper with medium stacking fault energy. In order to investigate the possible mechanical twinning of copper under a new type of high speed processing technique—electromagnetic forming, the pure copper was electromagnetically bulged followed by microstructural characterization through electron backscattered diffraction and transmission electron microscopy. The results revealed a reduction of twin boundaries with increasing plastic strain, indicates a non-twinning deformation mechanism which is different from the deformation twinning observed in other high speed forming process. The physical origin of the present phenomenon is discussed in detail according to the energy barrier and the critical shear stress that are required for the nucleation of perfect and partial dislocations that determine the formation of twins.

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