Al–Cu–Fe quasicrystals (QCs), characterized by a unique aperiodic atomic structure, are of considerable interest due to their unusual physical properties, including high hardness, low friction coefficient, and corrosion resistance. Synthesis of Al–Cu–Fe QCs by mechanical alloying (MA) and subsequent heat treatment (HT) is an effective approach to obtaining single-phase materials with controlled microstructural characteristics.
A mixture of elemental aluminum, copper, and iron powders with a given ratio of Al65Cu20Fe15 was processed in a planetary ball mill for five hours. Analysis of the phase composition of the ground samples revealed the presence of exclusively diffraction maxima corresponding to metallic components after an hour of processing. Long-term grinding contributed to the formation of a solid solution of Al (Cu, Fe), which is a β-phase, but the formation of an icosahedral quasicrystalline phase (i-phase) was not observed.
To initiate solid-phase transformations, the milled powders were subjected to heat treatment in the temperature range of 600–700 °C for four hours. The presence of the i-phase, β-phase, and ω-phase of Al7Cu2Fe1 was established in the samples processed in the mill for 5–45 minutes. The highest content of the i-phase was recorded after 15 minutes of milling followed by annealing at 700 °C, as well as after 30 minutes of milling and annealing at 650–700 °C. The annealed powders exhibit weakly expressed ferromagnetic properties at room temperature, while magnetic losses decrease with an increase in the proportion and size of the i-phase, as well as with a decrease in the content of the β- and ω-phases.
ML starts with mixing Al, Cu and Fe powders in a given stoichiometric ratio in a high-energy ball mill. The ML process results in intense plastic deformation and welding of the powder particles, forming a nanostructured composite. Long-term ML promotes the formation of a metastable amorphous or nanocrystalline state, which is a precursor for the subsequent formation of the CC phase.
ML is followed by thermal annealing, which is carried out at different temperatures and times for crystallization of the CC phase. The temperature and time of annealing have a significant effect on the phase composition, grain size, and degree of perfection of the CC structure. Optimal thermal annealing conditions allow obtaining single-phase CC materials with a high degree of icosahedral ordering.
Magnetic properties of Al–Cu–Fe CC are usually weak and may depend on the phase composition and the presence of magnetic impurities. Studies show that the Al–Cu–Fe CC phase is diamagnetic or has weak paramagnetism. The effect of ML and HT on magnetic properties is associated with changes in the microstructure, phase composition and the creation of defects in the CC lattice. Further studies are aimed at studying the effect of alloying elements and nanostructuring on the magnetic properties of Al–Cu–Fe CC to expand their application areas.
Author: Hoang Viet Nguyen, Nam Binh Do, Thi Hoang Oanh Nguyen, Cao Son Nguyen, Van Trung Trinh, Hong Thang Le & Alberto Moreira Jorge Junior
Institute: School of Materials Science and Engineering, Hanoi University of Science and Technology, Hanoi, 100000, Vietnam