Microstructure, Mechanical Response, and Tribological Behavior of Mechanically Alloyed and Microwave-Sintered...

In this study, AA7068 aluminum matrix composites reinforced with TiB₂/TiC were fabricated via mechanical alloying and microwave sintering to investigate the influence of reinforcement content and sintering temperature on microstructure, mechanical properties, and dry sliding wear. Mechanical alloying refined powders, reducing D₅₀ from 51.5 µm (AA) to 22.5 µm (AC9) and enhancing dispersion and retention of TiB₂/TiC particles. XRD confirmed α-Al as the dominant matrix phase, preserved TiB₂ and TiC phases, and limited MgAl₂O₄/ZnAl₂O₄ spinel formation. Crystallite refinement and increased lattice microstrain were observed with the addition of reinforcement. Microhardness increased with reinforcement content and sintering temperature, reaching 122.2 HV_0.05 in AC9-2. At the same time, the highest compressive strength was observed in AC6-2 (431.05 MPa), indicating that optimal load-bearing depends on densification and interfacial integrity rather than hardness alone. AC9-2 exhibited the best wear resistance, with a cumulative specific wear rate of 2.723 × 10^-4 mm³/Nm over 1000 m. SEM-EDS analysis revealed oxide-rich tribolayers, mechanically mixed layers, TiB₂/TiC fragments, and Fe-rich third-body debris, indicating wear is predominantly hardness-controlled but strongly influenced by microstructural factors. Overall, TiB₂/TiC hybrid reinforcement improves AA7068 wear resistance through combined hard-particle load-bearing, reduced penetration, tribolayer stability, and third-body effects, offering insight for high-performance hybrid aluminum composites.