OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 27 No. 1 2025 hybrid nanocomposites increases with increasing TiO2 content. However, because the Al matrix (2.7 g/cm³) contained reinforcing additives with higher densities, such as SiC (3.21 g/cm³) and TiO2 (4.23 g/cm³), the density of the hybrid nanocomposites was higher than that of the base aluminum matrix. Fig. 11 presents the results of the microhardness testing. As the figure shows, the hardness increases with increasing concentration of TiO2 nanoparticles. Adding 6 wt. % TiO2 to the Al- 7Si-based alloy increased its hardness from 69 HV to 92.5 HV. The higher hardness of the TiO2 nanoparticles compared to the pure matrix leads to an increase in the hardness of the Al- 7Si-based alloy composite with the addition of these nanoparticles. Saber et al. [14] also note that adding nanoparticles to a metal matrix alloy increases the hardness of the nanocomposites. This is because the uniformly distributed nanoparticles act as a reinforcing phase. The Orowan mechanism plays a major role in strengthening the composites, especially when the size of the reinforcing components is less than 100 nm [45]. According to this mechanism, the passage of a dislocation line through the ceramic TiO2 particles leaves a dislocation loop around the non-shearable TiO2 particles within the matrix. This prevents or decelerates the dislocation motion in the metal matrix alloys. According to Mahan et al. [11], adding 5 % TiO2 increases the Vickers hardness by 40 % compared to the original A2024 alloy. This effect is explained by the solid solution strengthening mechanism, in which TiO2 particles behave as obstacles to dislocation movement. Al-Jaafari [16] also demonstrated that adding 1.5 % TiO2 nanoparticles to AA6061 and AA6082 alloys as reinforcing components increases the Brinell hardness number (BHN) by 12.1 % for AA6082 and 32 % for AA6061. Fig. 11. Effect of TiO₂ wt. % on the hardness of Al-7Si matrix composites The wear test results indicate that the wear rate of the composites increased with increasing test load and decreased with increasing TiO2 nanoparticle content. As illustrated in Fig. 12, at a load of 10 N and a sliding distance of 350 m, the Al- 7Si-based alloy composite with 6 wt. % TiO2 demonstrated the lowest wear rate (0.017 mm3/m), while the Al- 7Si-based alloy showed the highest wear rate (0.028 mm3/m). This is explained by the presence of hard particles that increase the overall hardness of the material. A similar trend was observed at a load of 20 N. Fig. 13 demonstrates that the wear rate of the tested samples increased with increasing sliding distance. Thus, the Al- 7Si-based alloy (Fig. 12) demonstrated a wear rate of 0.028 mm³/m at a sliding distance of 350 m, while increasing the distance to 700 m (Fig. 13) resulted in a wear rate of 0.039 mm³/m. The same pattern was observed for the fabricated composite materials. Numerous researchers [4, 5, 7, 8, 15, 46] note that the influence of the applied load increases with the increasing percentage or size of the reinforcing particles. Walker et al. [46] explained this phenomenon by the intense abrasive wear of both contacting surfaces, resulting from the use of hard ceramic particles as reinforcement. Shashi et al. [15] studied the effect of TiO2 addition on the wear properties of AA2014
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