Mechanical alloying (MA) is an effective method for synthesizing quasicrystalline (QC) materials, particularly in Al–Cu–Fe systems. Formation of the QC phase during MA directly depends on the composition of the initial powder mixture. Minor deviations from the stoichiometric composition can significantly affect the rate of formation and stability of the QC phase.
Studies show that excess aluminum in the mixture promotes faster formation of the icosahedral phase. This is due to the increased diffusion mobility of Al atoms and the facilitation of the processes of structural rearrangement at the initial stages of ML.
A thorough study of the effect of component composition on the formation of quasicrystalline (CC) phases in Al-Cu-Fe powders obtained by mechanical alloying was carried out in this work. Microstructural analysis was performed using X-ray diffraction and transmission electron microscopy (TEM). The obtained data indicate that the formation of CC phases in the Al-Cu-Fe system is determined by the initial content of Al, Cu and Fe, while the Al70Cu20Fe10 composition demonstrates the best indicators among the studied samples. Despite the impossibility of obtaining a pure CC phase, achieving a high concentration of the CC phase is possible by optimizing the process parameters, such as milling duration, temperature and annealing duration. In particular, for powders of the Al70Cu20Fe10 composition, subjected to milling for 2 hours and subsequent annealing at 750 °C for 5 hours, the volume fraction of the CC phase exceeds 90%.
The concentration of copper and iron also plays an important role. The optimum ratio of Cu and Fe is necessary to stabilize the icosahedral structure. Deviations from this ratio can lead to the formation of crystalline intermetallic phases that compete with the QC phase.
In addition to the composition, the microstructure of the starting powders also affects the formability of the QC phase. Using powders with a smaller particle size promotes a more uniform distribution of elements and accelerates the alloying process. Preliminary heat treatment of the starting powders can also affect the reactivity of the mixture in the MA process.
Author: Shilong Yin, Caixia Li, Qing Blanc, Min Lu
Institute: College of Science, Huainan University, Nanjing, 210098, People’s Republic of China, Institute of Science, PLAUST, Nanjing, 211101, People’s Republic of China