Nanoquasicrystalline Al-Fe-Cr-Ti alloy matrix/γ-Al2O3 nanocomposite powders: The effect of the ball milling process

Quasicrystalline aluminium alloys and aluminium based nanocomposites with the advantage of high strength over commercial aluminium alloys have been studied for many years. In this work a nanoquasicrystalline Al-Fe-Cr-Ti alloy powder and a nanocomposite consisting of a mixture of a nanoquasicrystalline alloy and nanosize γ-Al2O3 powders were produced through mechanical milling with different milling speeds. It has been observed that a higher milling time or milling speed can improve the homogeneity of the γ-Al2O3 distribution. The α-Al crystallite size decreases and the hardness increases with the milling time. The smallest crystallite size (14 nm) and the highest hardness value (638 HV10g) were obtained for the nanocomposite after 30 h of milling at 250 rpm. As the α-Al crystallite size is the main change in the microstructure during the ball milling process, the change in the hardness of the milled powders was found to follow a Hall-Petch type relation with an exponent of 0.25.