High-energy ball milling (HEBM) is a powerful tool for inducing structural changes in materials, including quasicrystals. In this work, we investigated the decomposition process of single-phase icosahedral AlCuFe under HEBM using X-ray diffraction (XRD) and transmission electron microscopy (TEM).
At the initial stages of grinding, a broadening of the diffraction peaks is observed, indicating a decrease in the size of crystallites and accumulation of defects. Further grinding leads to the appearance of new diffraction peaks corresponding to crystalline phases. X-ray diffraction analysis showed that the main decomposition products are Al2Cu and FeAl.
For this study, the Al64Cu24Fe12 alloy was prepared by melting in an induction furnace followed by crystallization under standard casting conditions. In order to form an icosahedral phase (i-phase) within the single-phase region, the cast sample was heat treated at 700 °C under argon. The resulting i-phase was subjected to a milling process for different periods of time to evaluate its resistance to severe deformation.
X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) were used to analyze the structure of ball-milled powders. XRD results demonstrated that the size of quasicrystals decreases during mechanical ball milling for up to about 30 h. HRTEM analysis confirmed the presence of aperiodic nanoscale regions, including regions with a pronounced fivefold symmetry axis.
Therefore, the i-phase remains stable during the first 30 hours of grinding. However, with an increase in the mechanical grinding time from 30 to 50 hours, a gradual transition of the i-phase to the β-cubic phase is observed.
TEM studies confirmed the XRD results. High-resolution images identified Al2Cu and FeAl nanocrystals embedded in the amorphous matrix. Electron diffraction analysis revealed the presence of crystalline reflections corresponding to Al2Cu and FeAl, as well as a diffuse halo characteristic of the amorphous phase.
The obtained results demonstrate that VESHI leads to destabilization of the icosahedral structure of AlCuFe and its decomposition into more stable crystalline phases. The formation of Al2Cu and FeAl nanocrystals in the amorphous matrix indicates a complex mechanism of phase separation caused by a high defect density and chemical mixing induced by VESHI. These studies are important for understanding the processes of structural transformation in quasicrystals under mechanical loads and can be useful for the development of new nanomaterials.
Author: C. Patiño-Carachure, O. Téllez-Vázquez, G. Rosas
Institute: Institute of Metallurgical Research, UMSNH, Building U, University Campus, Morelia, Michoacan, 58000, Mexico