Influence of TiB₂ particle size on the microstructure and properties of Al matrix composites prepared via mechanical alloying and pressureless sintering

In this study, TiB₂ particulate reinforced Al matrix composites were fabricated with the incorporation of both micron- and submicron-scale TiB₂ particles by a combined method of mechanical alloying, cold pressing and pressureless sintering. Commercial TiB₂ powders with an average particle size of 40 μm were milled to 320 nm for 12 h in a high-energy ball mill. The effects of TiB₂ particle size (40 μm and 320 nm), TiB₂ content (5, 10 and 15 wt.%) and mechanical alloying duration (2, 4 and 8 h) on the microstructural and properties of the Al matrix composites were investigated. The composites reinforced with submicron TiB ₂ particles exhibited higher hardness (in the vicinity of 2 GPa for 15 wt.% reinforcement) and lower relative wear resistance values compared to those reinforced with micron-scale TiB₂ particles. Furthermore, hardness and relative wear resistance values of the composites increased with increasing TiB₂ contents. Density and hardness values of the sintered samples has uncertain tendency in regard of different mechanical alloying durations. Microstructures of the micron- and submicron-scale TiB₂ reinforced Al matrix composites contain homogeneously dispersed fine- and ultrafine-grained TiB₂ particles and an amount of Al₃Ti flakes.