Synthesis, structure and sinterability of 6061 AA100-x-x wt.% TiO2 composites prepared by high-energy ball milling

Manufacturing of 6061 Al alloy reinforced with different weight percentages of TiO2 metal matrix composite powder through low-energy and high-energy ball milling for microcomposites and nanocomposites respectively followed by cold uniaxial compaction and sintering was investigated. The milled powder was characterized by X-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy, and differential thermal analyzer. No intermetallic compounds were observed during high-energy ball milling by wet method, but petite iron contamination was present due to vial media after 40 h milling. The crystallite size of about 46 nm was obtained in the case of high reinforcement content. Powder surface morphology, crystallite size as a function of chemical composition and milling time, and lattice parameter of the high-energy ball-milled powder were examined. The effect of matrix-to-reinforcement particle size ratio on the green compressive strength for both composites was also investigated. The green pellets were degassed at 350 oC for 60 min, and then sintered in the temperature steps of 475, 550 and 625 oC under reducing atmosphere for 120 min. The effects of reinforcement content on densification as percentage theoretical density, sinterability and Vickers hardness of the composites were also studied. The results revealed that the sinterability improved as the percentage of reinforcement increased for nanocomposites whereas it worsened for microcomposites. The nanocomposites exhibited a high Vickers hardness of 1126 MPa, which was around 3-4 times higher than that of microcomposites.