**3. Effect of electroplasticity**

**Figure 5.** (a) Enlarged fragment of surface area of produced thermal grooves and (b) cross-sectional profile of surface

From **Figure 3**, it follows that as a result of multipulsed irradiation, the titanium surface locally becomes sufficiently more smooth than the initial one (surface roughness after surface mechanical polishing, stretching, and so on is smoothing; see **Figure 1b**). This is a well-known

The inverse knife-shaped metal groove can support the channel surface plasmon polariton (CSPP) propagation [3, 5, 18]. In considered geometry of experiment, the direction of quasigrating vector is orthogonal to laser radiation polarization *Et*. For efficient excitation of CSPP, the electric field strength component of incident radiation must be maximal. So, the metal surface covered with quasi-grating has anisotropic absorptivity due to CSPP excitation and dissipation of their energy into heat. It is known that micro- and nanostructured metal surface

Note that the effect of the electrons drag by surface plasmon polaritons becomes apparent in the surface current in metal skin layer [12, 15] and in the *lateral* flux of relativistic electrons in vacuum under the metal surface irradiation by exawatt laser power density (pulse duration

One may wait that the discovered effect may be well observable for powerful ultrashort laser pulse interaction with metals. Really, the experimental data for the multipulsed laser interaction with metals and alloys have been published for femtosecond pulse durations followed by quasi-grating **G** ⊥ **E** formation for titanium metal [21, 22] and Ti-based alloy Ti-Zr-Cu-Pd [23] without any suggestions about the origin of their appearance (see **Figure 6**). From our opinion the production mechanism of quasi-grating **G** superimposed on the **g** ∣∣ **E** resonant grating is analogous for one suggested for nanosecond irradiation regime. Note that the thermal etching groove formation is inherent to (poly)crystalline materials, but the alloy Ti-Zr-Cu-Pd is the amorphous one. In fact under the alloy heating up to high temperature, the alloy transfers from its metastable state to the crystalline one, and the suggested

result of material redistribution caused by surface atom diffusion [17].

obtained along white horizontal line of **Figure 4a**.

168 Study of Grain Boundary Character

also has anisotropy of electrical properties [19].

less than 1 ps) [20].

model works further.

The effect of electroplasticity will be considered in this section as one of the most closed volume analog for anisotropic grain boundary movement (AGM) effect (Section 2). At first the electroplasticity effect (EPE) in metals was discovered by Troitsky [25]. The metals demonstrate the enhanced plasticity under the influence of the high directed current density.

The high perfection of axial texture is formed due to metal grains of definite crystallographic orientations turned in the direction of wire dragging (**Figure 7**). The initial material takes the texture "suitable" for subsequent high current transfer [26]. This structure turns out more perfect than that formed by the usual wire-dragging technology. During electro-plastic wire dragging, the deformation strengthening fails and the plasticity increases as a result [27–35].

**Figure 7.** The perfect wire texture creation during electro-plastic wire dragging in condition of current density **j** and wire movement direction **P** vector coexistence [26].

The thorough analysis shows that the nonthermal current action mechanisms involve electroplastic effect and ponderomotive forces of pulsed current and impact the wire tension decrease sufficiently. More efficient pulsed current action (in comparison with dc) [26, 30], current polarity dependence evidence the nonthermal nature of the occurred processes. In addition, during rapid wire dragging (>10 m/s), the Stewart-Tolman effect takes place (the delay of free electron gas against crystal lattice accelerating in the area of metal deformation inside a drawing ring caused by transition to a smaller diameter). The Stewart-Tolman effect is electronic by nature, and it favors the axial wire texturing to the electro-plastic and its degree of perfection increasing. The typical parameters realized under the electro-plastic effect are listed below:


The observed effect is caused by plasticity influence of EPE in metal volume; it relieves the process of axial texture formation and decreases friction in dragging die due to the grain crush in the near-surface wire areas.

Apart from the perfect grain structure creation for copper, it was observed as follows [26]:

**•** The number of randomly distributed dislocations decreases.


For the stainless steel wire, it was observed as follows [26]:


The electroplasticity effect is a linear function of current density and was never observed for alternated current. It is known that to remove inner tension and residual deformations on highvoltage transmission equipment, the powerful pulse current is transmitted by the wires hanged preliminary before the wires are to be arranged finally.

So, in general, the electroplasticity effect may be considered as a volume analog of the effect of anisotropic grain boundary movement (AGM) being discussed. Really, the electroplasticity effect is caused by directed current of electrons' action. And the AGM effect is also the consequence of the direct current of electrons forced by the effect of electrons drag by surface plasmon polaritons in optical skin layer of metal. In both cases, the directed electrons transfer their momentums to the grain boundary as a wall and force their displacement.
