Structural investigations of the Al50Fe25Ti25 powder mixture mechanically alloyed under various conditions

Abstract

The aim of this work was to study the structural and phase transformations that take place during mechanical alloying of the ternary Al50Fe25Ti25 alloy in a high-energy planetary ball mill. Two experiments were performed: one with addition of ethanol and the other without any additional agent. The structural changes and the formation of new phases occurring in the material during mechanical alloying at various milling times were examined using X-ray diffractometry (XRD), differential scanning calorimetry, conventional transmission electron microscopy and high-resolution electron microscopy. The XRD patterns show that a b.c.c. Fe(Al) solid solution and an fcc phase with the lattice parameter a 0=4.295 Å isomorphous with TiC are the final products of the process performed with addition of ethanol. Electron microscopy observations reveal that after the longest milling time, the structure of the powder particles becomes nanocrystalline. No phase changes were found in the XRD pattern of the final product of ethanol-added milling, annealed at 720°C for 2 h. The milling process performed without addition of ethanol leads to an amorphous phase. Heating of this phase in a calorimeter causes crystallisation of the ternary τ 2 phase (Al 2FeTi) and an Fe(Al,Ti) solid solution.