## 3 Results and Discussion
### Structure and Hardness
Figure 4 shows the structure of the composite consisting of Al solid solution dendrites 15-20 \(\upmu\)m in size, with clearly defined degenerate eutectics ((Al) + Al\({}_{13}\)Fe\({}_{4}\)) along their boundaries (Figure 4a) and needle-shaped primary crystals of Al\({}_{13}\)Fe\({}_{4}\) 10-40 \(\upmu\)m long and 1-3 \(\upmu\)m wide (Figure 4b). Figure 4c,d show the microstructure of the AlFe alloy. The comparison of the composite microstructure with that of the matrix alloy shows that the addition of graphene did not result in the change in the volume fraction, the density of distribution, size, or morphology of the main structural constituents. The evolution of the structure under HPT was studied using two structural analysis techniques: scanning and transmission electron microscopy. The backscattered electron images indicate that deformation resulted in the structural refinement of the main constituents in the materials investigated and changed their forms and sizes. The pertinent backscattered electron image of the structure shows the evolution of the shape and size of Fe aluminides in the process of deformation with the increase in n (Figure 5). HPT induced the breakage and fragmentation of the primary needle-like Al\({}_{13}\)Fe\({}_{4}\) precipitates, with the formation of more equiaxed crystals closer to eutectic crystals in size. As a result of mass transfer upon applying HPT (n = 10), the particles of iron aluminides are evenly distributed in the volume of the sample, and the average size of all Fe-containing phases decreased to 0.58 \(\upmu\)m (Figure 5b,c). Figure 3: Thermal conductivity of the AlFe alloy and AlFeGn composite. Figure 4: Microstructure of the as-cast AlFeGn composite (**a**,**b**) and as-cast AlFe alloy (**c**,**d**). Figure 5: Backscattered electron images of the microstructure of the as-cast (**a**) and HPT-deformed n = 5 (**b**) and n = 10 (**c**) AlFeGn composites. XRD analysis showed that the addition of graphene did not affect the phase composition of the matrix, and the diffraction patterns of the AlFe alloy and AlFeGn composite in the as-cast and deformed states were identical. Figure 6 shows a comparison of sections of diffraction patterns for the as-cast and deformed composites. The range of 20 was chosen to show the most intense reflections from the detected phases, i.e., the Al solid solution and the Al\({}_{6}\)Fe and the Al\({}_{13}\)Fe\({}_{4}\) aluminides. The Al\({}_{6}\)Fe phase presumably belongs to eutectic aluminides. The indexing of diffraction reflections in the range of angles 20 = 18-145\({}^{\circ}\) did not reveal any additional structural components of the composite. Reflections from the Al\({}_{6}\)Fe and the Al\({}_{13}\)Fe\({}_{4}\) phases are clearly visible in the diffraction pattern of the as-cast composite. The intensity and number of reflections from these phases decreased in the diffraction pattern of the deformed composite since the aluminides were crushed and partially dissolved during HPT. The transmission electron microscopy (TEM) images clearly show structural changes in the matrix when the composite was subjected to HPT. The results for the AlFeGn composite after HPT (n = 10) are given below. According to Figure 7a,b, HPT induced a rather uniform ultrafine-grained (UFG) structure consisting of grains from 90 to 450 \(\upmu\)m in size. The grain-subgrain size distributions indicate that the minimum-sized grains of 90 nm make up 7%. (Figure 8). The percentage of large crystals 390-450 nm in size does not exceed 10%, and most of the grains have a size of 150 to 250 nm. Figure 6: Diffraction patterns of AlFeGn in the as-cast and deformed (HPT n = 10) states. Figure 7: The microstructure of AlFeGn composite: bright-field image (**a**); dark-field image in (111)\({}_{\rm Al}\) and (200)\({}_{\rm Al}\) reflections (**b**); SAED pattern (**c**). The shape of most of the grains is close to equiaxial.