Intermetallic phases produced by the heat treatment of mechanically alloyed AlMo powders

The thermal behaviour of Al- xat.%Mo ( sx=, 10, 17, 20, 27, 50 and 75 powders mechanically alloyed in a conventional ball mill was investigated by differential scanning calorimetry, differential thermal analysis and X-ray diffraction. The temperature and heat of the solid state reactions leading to the formation of intermetallic phases markedly varied with milling time owing to significant microstructural changes occurring during milling. The intermetallic phases Al 2Mo, Al 5Mo, Al 4Mo, Al 8Mo 3 and AlMo 3 were identified as reaction products. The solid state reactions were discussed in terms of nanocrystalline structures created by mechanical alloying. After 1000 h of mechanical alloying, powders of various nominal compositions exhibited remarkably different microstructural parameters, i.e. crystallite size, intercrystalline (amorphous phase) volume fraction and intercrystalline thickness as well as intercrystalline composition. The most important factors affecting the change in thermal behaviour with milling time were suggested to be the reduction in crystalline size and increase in the intercrystalline volume fraction.