T.A. Sviridova

Crystallochemical aspects of solid state reactions in mechanically alloyed Al–Cu–Fe quasicrystalline powders

Abstract A number of elemental mixtures having initial compositions close to Al65Cu23Fe12 were mechanically alloyed at different energy intensities using a planetary mill. Laboratory X-ray diffraction analysis, differential scanning calorimetry and Mossbauer spectroscopy were used for characterization of the phase and structural state of mechanically alloyed powders after different periods of milling and annealing. Several exothermic effects were found, and these were ascribed to specific solid-state reactions. Quantitative phase analysis was applied in order to identify the mechanism of solid-state reactions taking place in the vicinity of the quasicrystalline phase domain in the Al–Cu–Fe system as a result of mechanical and thermal excitation and homogenization. Metastable intermetallics were identified which possess certain structural and topological elements identical to those found in quasicrystals.

The Evolution of Crystalline Precursors During the Formation of Al-Cu-Fe Quasicrystalline Intermetallics in Mechanically Alloyed Powders

Mechanical alloying (MA) of elemental powders in the Al-Cu-Fe system was carried out using two types of laboratory equipment (vibratory and planetary mills) to produce single phase, stable icosahedral quasicrystals. The sequence and nature of the solid state reactions during milling and subsequent annealing were studied in detail using qualitative and quantitative laboratory X-ray analysis and differential scanning calorimetry. The effect of milling parameters (energy intensity, temperature, milling time) on the course of transformations was elucidated. Specific reactions were identified which took place during annealing in different temperature ranges. The evolution of crystalline precursors of the quasicrystalline phase was established.

Use of mechanical alloying and subsequent annealing for obtaining intermetallic compound CuAl2

The possibility of obtaining a “line” (narrow-homogeneity-range) intermetallic compound CuAl2 with the use of mechanical alloying (MA) and subsequent annealing has been investigated by X-ray diffraction and scanning electron microscopy. Regimes (composition of a charge mixture, time of preliminary MA, time and temperature of annealing) allowing one to obtain a virtually single-phase compound have been determined. The low-temperature annealings in a temperature range of 100–250°C have shown that the most probable mechanism of mass transfer upon heating of layered composites obtained by MA is grain-boundary diffusion, which can be explained by a large fraction of grain boundaries in mechanically alloyed powders.