# Al-Fe-Ni Metallic Glasses via Mechanical Alloying and Its Consolidation
## 3 Results and Discussion
To investigate the structural changes of the as-milled powder particles (60 h MA) under the crystallization temperature as observed on the DSC curves, the alloys were annealed at 480, 600 and 700 \({}^{\circ}\)C. The XRD patterns of the annealed powders are presented in Figure 7. The onset crystallization temperature is considered to be the nucleation stage for crystallization, while the peak temperature corresponds to the growth of nuclei [48; 49]. The alloys are heated beyond the peak temperature where the presumed phases at this stage are those crystallized. After annealing the amorphous alloy powders to 480 \({}^{\circ}\)C, the diffraction peaks corresponded to cubic Al together with the residual amorphous phase. For an amorphous alloy prepared at 250 rpm (as seen in Figure 7a), a peak of the AlFe\({}_{3}\) phase was also detected after annealing at 480 \({}^{\circ}\)C. Further increasing the annealing temperature beyond the secondary peak crystallization temperature resulted in the disappearance of the residual amorphous peak. The formation of an Al\({}_{75}\)Ni\({}_{10}\)Fe\({}_{15}\) (PDF#42-1042) metastable phase besides the AlNi and AlFe\({}_{3}\) phases was also observed in both alloys after annealing at 600 \({}^{\circ}\)C. The Al\({}_{75}\)Ni\({}_{10}\)Fe\({}_{15}\)'s formation is remarkable as a quasicrystal phase that decomposes into intermetallics when the annealing temperature is raised to 700 \({}^{\circ}\)C for both the 250 and 350 rpm milling modes. As a metastable phase, it can be decomposed into the AlNi phase in the Ni-rich regions and the Al\({}_{13}\)Fe\({}_{4}\) phase in the Fe-rich regions when the temperature is raised and energy is provided beyond the enthalpies of mixing \(\Delta\)H values [50]. The phases produced during the annealing of two amorphous alloy powders (milling at 250 and 350 rpm) at 700 \({}^{\circ}\)C include Al (PDF#04-0787), Al\({}_{13}\)Fe\({}_{4}\) (PDF#29-0042) and AlNi (PDF#20-0019). The analysis of the crystallization of Al\({}_{82}\)Fe\({}_{14}\)Ni\({}_{4}\) amorphous alloys powders after heat treatment indicates that the phases precipitated from the amorphous phase may be correlated with the milling speed: primary crystallization in amorphous alloys milled at 350 rpm and eutectic crystallization in amorphous alloys milled at 250 rpm. The strong chemical interactions of higher milling speeds can change the short-range order to more stable configurations. At the same composition of Al\({}_{82}\)Fe\({}_{14}\)Ni\({}_{4}\), amorphous alloys milled at 250 rpm seem to be an easier arrangement of the atoms to become crystalline in structure compares with those of amorphous alloys milled at 350 rpm. Figure 6: DSC curves of Al\({}_{82}\)Fe\({}_{14}\)Ni\({}_{4}\) powders milled at 250 and 350 rpm for 60 h using a heating rate of 20 K/min. Amorphous Al\({}_{82}\)Fe\({}_{14}\)Ni\({}_{4}\) powders milled at 350 rpm were selected for SPS consolidation due to their higher thermal stability compared with that of 250 rpm. Based on the DSC curve shown in Figure 6, the sintering temperatures chosen were within the exothermal peaks. Consolidation of mechanically alloyed powders was performed on a spark plasma sintering to produce bulk samples. The sintering temperature was selected based on the results of the DSC thermal analysis and the shrinkage behavior of the sample during sintering [33]. Figure 8 exhibits the change in shrinkage (obtained by Z-displacement) of amorphous Al\({}_{82}\)Fe\({}_{14}\)Ni\({}_{4}\) powder during sintering at 600 \({}^{\circ}\)C under a pressure of 300 MPa. The degree of shrinkage increased as the sintering temperature increased. The shrinkage went up to 400 \({}^{\circ}\)C and held steady up to 570 \({}^{\circ}\)C. The shrinkage increased to 600 \({}^{\circ}\)C throughout the holding time. During the holding time, the viscosity of the sample decreased and the mobility of the atoms increased, resulting in an increase in sample shrinkage. [PERSON], S et al.