Rahul Gupta

This study investigates the influence of nano-sized reinforcements on aluminum matrix composites’ mechanical and tribological properties. Microstructural analysis revealed that introducing nanoparticles led to grain refinement, reducing the grain size from 129.7 μm to 41.3 μm with 2 wt.% TiO₂ addition. Furthermore, ultrasonic-assisted squeeze casting of AA6061 composites reinforced with TiO₂ and Al₂O₃ resulted in a 52% decrease in grain size, demonstrating nano-reinforcements’ effectiveness in refining the matrix structure. Despite these advantages, the high surface energy of nanoparticles causes agglomeration, which can undermine composite performance. However, ultrasonic-assisted stir casting reduced agglomeration by approximately 80% compared to conventional stir casting, and cold isostatic pressing improved dispersion uniformity by 27%. The incorporation of nano-reinforcements such as SiC, Al₂O₃, and TiC significantly enhanced the material properties, with hardness increasing by ~30% and ultimate tensile strength improving by ~80% compared to pure Al. The hardness of nano-reinforced composites substantially rose from 83 HV (pure Al) to 117 HV with 1.0 vol.% CNT reinforcement. Additionally, TiC-reinforced AA7075 composites improved hardness from 94.41 HB to 277.55 HB after 10 h of milling, indicating a nearly threefold increase. The wear resistance of Al-Si alloys was notably improved, with wear rates reduced by up to 52%, while the coefficient of friction decreased by 20–40% with the incorporation of graphene and CNT reinforcements. These findings highlight the potential of nano-reinforcements in significantly improving the mechanical and tribological performance of n-AMCs, making them suitable for high-performance applications in aerospace, automotive, and structural industries.

In this work, high-temperature tribological characteristics of ilmenite-reinforced LM13 aluminum alloy–based matrix composites (AMCs) and boron carbide–reinforced AMCs are compared. Stir-cast composites were processed using boron carbide (covalently bonded discontinuous particles (CDP)) and ilmenite (natural discontinuous particles (NDP)) particles separately as reinforcements. The particle size range was 106–125 µm, and reinforcement levels were 5, 10, and 15 wt% for both types of composites. Both composites exhibited a uniform distribution of reinforced particles and grain refinement. Compared to the LM13 base alloy, NDP composite containing 15 wt% reinforcement showed significant improvement in hardness (57%), coefficient of friction (57%), mild-to-severe wear transition temperature, average steady-state wear-rate (49%), and coefficient of thermal expansion (55%). CDP-15 composite showed slightly better properties than NDP-15 composite. Microstructure refinement, increased dimensional stability, formation of the oxide layer, and formation of tribolayer due to reinforcement of the ceramic fillers were the main reasons for the improvement in properties of processed AMCs. Scanning electron microscope (SEM)-energy dispersive spectroscopy (EDS) of wear tracks-debris showed abrasive/delamination wear as the main mechanism for materials loss. The research showed that the low-cost ilmenite particles can substitute for the very costly boron carbide particles as reinforcements in AMCs used for dry sliding wear applications under high operating temperatures–applied load conditions of the order of 300 °C–49 N.