**4. Temperature effect on dislocation fractal structures**

The mechanical properties of metals are highly influenced by temperature. In general, the mechanical strength decreases significantly, and the ductility and plastic deformation increases with temperature. In addition to these effects, when T > 0.5Tmelt, time-dependent plasticity becomes dominant [31]. This time-dependent deformation is also called creep. In this temperature range, the dislocations increase their mobility due to the activation of the climbing mechanism, in particular when the staking fault energy is high. The activation of dislocation climbing is revealed in the appearance of well-ordered dislocation structures generated during deformation.

In the following section, some examples of dislocation structures generated at room temperature and high temperature (573 K) will be shown. In the second case, the temperature effect on the arrangement of dislocations to form subgrain boundaries will be observed.

conditions where images from one single mode, bright or dark, are enough for a complete description of the microstructure. In particular, after mechanical testing conducted at high temperature, the dislocation substructure is easily observed in

*TEM image of a magnesium alloy deformed at 3% at room temperature and a strain rate of 10*�*<sup>3</sup> s*

Finally, it is interesting to point out that TEM images have a 2D nature, whereas dislocations, twins, subgrains, and, in general, the crystal structure have a 3D nature. Cui and Ghoniem [13] studied the influence of size on the fractal dimension of dislocation structure throughout dislocation dynamics simulations. The analysis showed that the DF of the 3D structure is significantly smaller than the DF of the 2D corresponding to the projected dislocations in all considered sizes. **Figure 5** shows two images of a 3% deformed magnesium alloy at room temperature of the same area

*Bright field image of a magnesium alloy deformed at 3% of plastic strain at room temperature. (a) Sample fully*

*parallel to the beam and (b) sample tilted with respect to the previous condition.*

�*1*

*. Zone axis*

bright field mode because the lattice distortion is almost eliminated.

*[1120] g = [1101]. (a) Dark field and (b) bright field.*

*Fractal Analysis - Selected Examples*

**Figure 4.**

**Figure 5.**

**110**
