Nanostructure formation in the surface layer of metals under influence of high-power electric current pulse

The possibility to tailor the microstructure of metals is explored utilising a skin-effect for surface treatment. The theoretical simulation of the electric and magnetic fields in a metallic cylinder shows that melting followed by rapid quenching can occur in a skin layer of 5-10-mu m thickness if the amplitude of a single electric pulse of several nanoseconds duration is of the order of hundreds kiloamperes. The experiments using the SUS304 stainless steel show that besides a thin amorphous layer, a specific nano-twin structure can form at the near-surface region. The appearance of nano-twins is explained considering the stress components arising at the surface layer and in the bulk of the specimen during shock wave propagation caused by temperature gradients and the Lorentz force. It is shown that the high stress amplitudes can arise locally, furnishing the required conditions for twin nucleation and resulting in intensive plastic deformation of the sub-surface layer.