## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Material/State** & **Lattice** & **Crystallite Size** & **Microstrain** & **Dislocation** & **Microhardness** \\  & **Parameter (nm)** & **(nm)** & **(\%)** & **Density (m\({}^{-2}\))** & **(HV0.05)** \\ \hline Al-5 TiO\({}_{2}\)-2 PCA & & & & & \\ as-milled & 0.4047 & 30 & 0.11 & 4.3-10–14 & 162 \(\pm\) 4 \\ \hline hot-pressed & 0.4051 & 53 & 0.16 & 3.5-10–14 & 187 \(\pm\) 15 \\ \hline Al-5 TiO\({}_{2}\)-5 Cu & & & & & \\ as-milled & 0.4043 & 28 & 0.19 & 7.9-10–14 & 291 \(\pm\) 14 \\ \hline hot-pressed & 0.4049 & 60 & 0.18 & 3.5-10–14 & 233 \(\pm\) 22 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Microstructural parameters of the aluminum matrix obtained by XRD analysis and microhardness for different materials. supersaturated solid solution. Thus, the higher hardness of the material with the addition of copper is caused by a large number of hardening particles. To confirm the formation of aluminum carbide particles (Al4C3) in the hot-pressed material with the addition of stearic acid, a fine microstructure study was carried out using TEM. Figure 7a shows that the material's structure is nanocrystalline with a grain size of less than 100 nm, which confirms the X-ray diffraction data (Table 2). In addition, nanoparticles (shown by arrows) with a lamellar shape typical of the Al4C3 phase were found in the structure. Such nanorod-like particles were observed in mechanically alloyed materials if stearic acid was used as a PCA [69]. Moreover, the possibility of the formation of this phase was shown in our previous work [65]. The parameters of the microstructure affect the strength parameters not only at room temperature but also at elevated temperatures. The ability of the studied materials to withstand stresses at elevated temperatures was evaluated using compression tests at 300 \({}^{\circ}\)C. Compression diagrams are shown in Figure 8. It can be seen that the compression curve of the Al-5 TiO2-2 PCA material lies much higher than that for Al-5 TiO2-5 Cu. Thus, the yield and strength limits of the Al-5 TiO2-2 PCA material are 231 and 263 MPa, and for Al-5 TiO2-5 Cu143, and 153 MPa, respectively. That is, the strength of the former material is 1.7 times higher than that of the latter one, although the hardness of the material with the addition of stearic acid is, on the contrary, lower (Table 2). Annealing this material at 400 \({}^{\circ}\)C for 5 h decreases the strength parameters, yet they remain above 200 MPa. The high  
Figure 6: SEM images of hot-pressed composites with additions of (**a**) 2% stearic acid and (**b**) 5% Cu. Figure 7: Bright-field TEM images of the hot-pressed sample with addition of 2% stearic acid: (**a**) nanocrystallite structure, and (**b**) lamellar nanoparticles of Al4C3. thermal stability of the material with the addition of PCA should be due to dispersed Al\({}_{4}\)C\({}_{3}\) particles formed as a result of the decomposition of stearic acid. The low thermal stability of the material with the addition of copper is associated with the low strengthening efficiency of Al\({}_{2}\)Cu stable phase dispersoids precipitating at the pressing temperature. In order to form reinforcing particles of metastable modifications typical of Al-Cu alloys, the hot-pressed Al-5 TiO\({}_{2}\)-5 Cu material was subjected to quenching and subsequent aging in conventional mode (540 \({}^{\circ}\)C, 5 h + 180 \({}^{\circ}\)C, 8 h). However, the strength indicators of the aged material with the addition of copper turned out to be even lower than those for the hot-pressed one. This is due to a significant coarsening of the grains due to exposure to a high quenching temperature, with the average grain size reaching 231 nm. Thus, the grain size contributes more to the strength at elevated temperatures than the size and shape of the Al\({}_{2}\)Cu dispersoids. Furthermore, the addition of stearic acid to the Al-5 TiO\({}_{2}\) material has a more significant positive effect on its thermal stability than the addition of copper.