## 3 Results  
### Microstructural Analysis by Scanning Electron Microscopy  
Figure 2 presents the morphology of the elemental starting powders before the ball milling process. These powders correspond to Al and Fe40 Al, respectively. Figure 2a displays the irregular-shaped particles of Al (with a mean particle size of 2.7 microns \(\pm\) 0.95). Figure 2b exhibits the irregular-shaped Fe40 Al intermetallic particles (with a mean particle size of 27 microns \(\pm\) 2.9). Figure 3 presents the evolution of the particle morphology and size of the powder mixtures of Al-5 Fe40 Al, Al-10 Fe40 Al, and Al-15 Fe40 Al respectively. Aiming to improve the visibility and synthesize the results of the particle size, the micrographs corresponding to 0, 2, 4, and 8 h of milling taken from each composition (Al-5 Fe40 Al, Al-10 Fe40 Al, and Al-15 Fe40 Al), are presented in one figure. The scanning electron micrographs show that the particle size decreased as the milling time advanced from 0 to 8 h in the cases of the Al-10 Fe40 Al and Al-15 Fe40 Al powder mixtures. However, the particle size of Al-5 Fe40 Al underwent a progressive diminution from the beginning to the end of the processing. In addition, according to these micrographs, the particle morphology remained irregular. Figure 2: Scanning electron micrograph of (**a**) Al powder particles and (**b**) Fe40 Al intermetallic powder particles. Particle size distributions of (**c**) Al and (**d**) Fe40 Al. Figure 3: Microstructural evolution of the Al-5 Fe40 Al powder mixture composition as a function of milling time: (**a**) 0 h, (**b**) 2 h, (**c**) 4 h, (**d**) 8 h. Al-10 Fe40 Al: (**e**) 0 h, (**f**) 2 h, (**g**) 4 h, (**h**) 5 h. Al-15 Fe40 Al: (i) 0 h, (j) 2 h, (**k**) 4 h, (l) 6 h.  
In Figure 4, the particle size variation of the Al-5 Fe40 Al composite powder is presented. It can be observed that the mean particle size decreased from around 4.7 microns to 1.6 microns as the powder mixture was milled from 1 h to 4 h. Between 4 h and the end of the milling process, the particle size increased from 1.6 \(\upmu\)m to 2.4 \(\upmu\)m. This behavior could be related to the predominance of welding among the particles. The size ranges of the powder composite mixtures exhibited a slight tendency to narrow with the advancement of the processing time. Additionally, in Figure 4, the particle size of the Al-10 Fe40 Al powder mixture and the standard deviation as a function of the milling period are presented. This plot shows that the particle size predominantly diminished from about 4.1 \(\upmu\)m to 0.8 \(\upmu\)m as the milling time progressed from 1 h to 8 h. The size ranges related to the standard deviation of the powder composite mixtures exhibited a very slight trend to decrease with the advancement of the ball milling time. Figure 4 also shows the particle size of the Al-15 Fe40 Al powder mixture. In this plot, the particle size of the Al-15 Fe40 Al powder mixture decreased from 4.2 \(\upmu\)m at 0 h to 2.8 \(\upmu\)m at 8 h of ball milling. Similarly, the particle size distributions were applied to determine the mean particle size and the size range of the powder particles in each specimen. The size ranges of the powder composite mixtures suggest an almost imperceptible propensity to decrease as the ball milling period progressed. It is evident that the particle size variation as a function of milling time exhibited a similar trend for the processing of the three powder mixtures (Al-5 Fe40 Al, Al-10 Fe40 Al, and Al-15 Fe40 Al). This tendency indicates that extended milling times yield a more uniform size of powders and smaller mean particle sizes. Since the constituents of a powder mixture are ductile-brittle components, in this case, at the beginning of milling, the irregular shapes of the ductile aluminum particles were transformed into a flat flake morphology by the ball-powder-ball collisions, while the fragile particles corresponding to the Fe40 Al intermetallic compound were fragmented.