The formation of the icosahedral phase (i-phase) in the ternary Al–Cu–Fe system by cold deformation and subsequent annealing of elementary multilayer structures (EMS) is studied. MSSs consisting of alternating layers of Al, Cu, and Fe were obtained by magnetron sputtering onto substrates. The layer thickness was varied to achieve different stoichiometric compositions close to Al62Cu25.5Fe12.5, which is optimal for the formation of a stable i-phase.
Cold deformation of the MCC was carried out by drawing and rolling methods, which led to a significant decrease in the layer thickness and an increase in the defect density. Structural changes induced by deformation were studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM). It was found that deformation leads to mixing of layers at the atomic level and the formation of a nanocrystalline structure.
The formation of the icosahedral phase and the accompanying structural changes in the ternary Al–Cu–Fe system were studied using multiple cold rolling and folding (CR&F) of elementary foils of a given composition AlCu25Fe12.5 (at.%). At the initial stages of CR&F processing, the iron foil was uniformly distributed in the aluminum and copper layers. Upon reaching 40 rolling and folding cycles, the appearance of the Al2Cu phase was recorded, however, despite a further increase in the CR&F cycles, ternary phases were not detected. A stable icosahedral phase (i-phase) was formed after isothermal annealing of the samples subjected to CR at temperatures of 650 and 750 °C. The dynamics of phase transformations during multiple cold deformation and annealing of the Al–Cu–Fe system, as well as during heat treatment, is considered in the context of the formation and dissolution of the Al2Cu and Al7Cu2Fe phases.
Subsequent annealing of the deformed MCCs was carried out in the temperature range from 400°C to 800°C. XRD and TEM showed that at certain annealing temperatures, the i-phase is formed. The optimal annealing temperature for achieving the maximum content of the i-phase depends on the degree of preliminary deformation and the composition of the MCC. The mechanism of i-phase formation includes diffusion mixing of elements and nucleation and growth of icosahedral clusters.
The obtained results demonstrate the possibility of synthesizing the i-phase in the Al–Cu–Fe system by controlled cold deformation and annealing of the MCC. This approach allows obtaining materials with unique properties due to the presence of the icosahedral structure, such as high hardness, low friction coefficient and high corrosion resistance.
Author: J. S. Park, E. Fleury, J.-H. Kim, H. J. Chang, W. T. Kim, D. H. Kim, S. Yi
Institute: Center for Non-Crystalline Materials, Department of Metallurgical Engineering, Yonsei University, 134 Shincheon-dong, Seodaemun-gu, Seoul 120-749, South Korea, Center for Advanced Metallurgical Research, KIST, Seoul 130-650, South Korea, Department of Applied Physics, Jeonju University, Jeonju 360-764, South Korea, Department of Metallurgical Engineering, Kyungpook National University, Daegu 702-701, South Korea