Microstructure characteristics in Al-C system after mechanical alloying and high temperature treatment

In this work elemental powders of Al and 2 wt-% graphite were mechanically alloyed in a high energy horizontal attritor under purified argon atmosphere for 0.5-2 h. Powder mixes were then cold pressed at 1200 MPa and sintered at 550degreesC for between 2-32 It under the same protective atmosphere. Structural evolution was characterised by X-ray diffraction, scanning electron microscopy and transmission electron microscopy techniques. Results revealed that mechanical alloying was very effective in pulverising the powder mix, where after 2 h, the mix was fine enough to oxidise rigorously when exposed to open air. In general however, mechanical alloying was found to be inefficient to synthesise At with C. But after sintering, Al4C3 phase nanosized particles were formed in the microstructure. When the duration of sintering was prolonged, the particle population multiplied in number. Hence because of improvement in dispersion strengthening, the room temperature hardness of the material increased gradually.