Marek Krasnowski

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 A 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 2 FeTi) and an Fe(Al,Ti) solid solution.

Phase Transformation in Al3Ni2 Alloy during Mechanical Alloying and Heating of Milling Products

An elemental powder mixture corresponding to the Al3Ni2 phase stoichiometry was subjected to mechanical alloying in a high-energy ball mill. Products of this process after various milling times were investigated by differential scanning calorimetry. The phase transformations occurring in the material throughout milling and during heating in a calorimeter were investigated by X-ray diffraction method. This study revealed that a metastable nanocrystalline NiAl intermetallic phase was formed during the mechanical alloying process. Heating of the synthesised powders in the calorimeter caused phase transformations, the product of which was an equilibrium Al3Ni2 intermetallic phase or a mixture of NiAl, Al3Ni2 and Al3Ni intermetallic phases, depending on the milling time and the temperature up to which the material was heated.