Effect of Processing on Mechanically Alloyed and Spark Plasma Sintered Al-Al₂O₃ Nanocomposites

Metal matrix nanocomposites are advanced materials developed using ceramic nanoreinforcements and nanocrystalline metal matrices. These composites have outstanding properties and high potential for large number of functional and structural applications. In this work, nanocrystalline aluminium and Al-Al₂O₃ nanocomposites were synthesised using mechanical alloying and consolidated through spark plasma sintering technique. Scanning electron microscopy, X-ray diffraction, and mapping were used to characterize the powders and sintered samples. Density and hardness of sintered samples were measured using densimeter and hardness tester, respectively. It was found that milling of pure aluminium for 24 h reduced its crystallite size to less than 100 nm. For Al-Al₂O₃ nanocomposites, milling for 24 h decreased the crystallite size of the aluminium phase and resulted in uniform dispersion of the reinforcement. Sintering of the synthesised powders led to grain growth. Al₂O₃ contributed to growth inhibition when samples were sintered for 20 minutes and improved the hardness but reduced densification. The Al-10 vol.% Al₂O₃ nanocomposite had the highest Vickers hardness value of 1460 MPa.