*3.4. Dislocation Density*

From the center to the edge of the HPTE-processed rod, the GND density in copper after HPTE was 10-times higher when compared to that of the annealed material and it gradually increased from <sup>100</sup> <sup>×</sup> <sup>10</sup><sup>12</sup> <sup>m</sup>−<sup>2</sup> to 130 <sup>×</sup> <sup>10</sup><sup>12</sup> <sup>m</sup><sup>−</sup>2. (Figure 7). Total dislocation density derived from XRD measurements was higher (150 <sup>×</sup> 10<sup>12</sup> m−<sup>2</sup> in the central areas and 300 <sup>×</sup> 10<sup>12</sup> m−<sup>2</sup> at the edge, Figure 7), being that X-ray diffraction data accounted for both GND and SSD.

**Figure 7.** Dislocation density distribution in the CP Cu rod before and after HPTE.

### *3.5. Microhardness*

In agreement with microstructural observations and dislocation density measurements, the microhardness of the HPTE-processed copper increased from initial value of 75 HV to 110 HV in the central area, and to 125 HV at the mid-radius and at the edge of the sample (Figure 8a). It can be seen that at a distance of ~0.4 R from the center, microhardness reached its saturation value of ~125 HV and it remained roughly the same up to the specimen edge (Figure 8a).

**Figure 8.** (**a**) Microhardness distribution along the radius and (**b**) tensile curves of Cu before and after HPTE.

Therefore, according to the HV data, the Cu rod samples produced by HPTE consisted of two distinct regions, i.e., an inner and an outer region. There are: (1) a central region that extends up to ~0.4 R = 2.0 mm (corresponding equivalent strain ~8, Figure 8a) with a gradually increasing microhardness; and (2) an outer region (>0.4 R) with saturated microhardness value of about 125 HV. The tensile test samples had the gauge diameter of 6.85 mm, sampling both the central area and half of outer area, as indicated by a vertical line in Figure 8a.
