Mechanical alloying is an effective method for obtaining metastable phases, including quasicrystals. In this paper, the process of formation of the icosahedral phase in the Al-Cu-Fe system using mechanical alloying and subsequent heat treatment is investigated.
To study the elemental composition and chemical state of the surface of powders obtained by mechanical alloying, the X-ray photoelectron spectroscopy (XPS) method was used. Analysis of the XPS spectra showed the presence of Al, Cu and Fe, as well as oxygen, which indicates the formation of an oxide film on the surface of the particles.
Changes in the structure of Al70Cu20Fe10 ternary powders obtained by mechanical alloying were investigated using X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAFS), taking into account the duration of milling and subsequent heat treatment. During milling, it was found that only copper (Cu) is able to penetrate into the crystal lattice of aluminum (Al), forming an Al2Cu compound or an AlCu solid solution. This process depends on the duration of milling. Iron (Fe), in turn, retains its original structure of a body-centered cubic lattice (bcc α-Fe).
Heat treatment at 700 °C for 4 hours promotes the interaction of α-Fe with the formed Al2Cu compounds and the AlCu solid solution. The main products of annealing of the Al70Cu20Fe10 sample after 10 hours of grinding and the Al70Cu20Fe10 sample after 40 hours of grinding are icosahedral quasicrystals Al65Cu20Fe15. Local structural distortions in the vicinity of Fe and Cu atoms in the icosahedral phase are approximately 50% higher than similar distortions in the Al(Cu, Fe) solid solution.
X-ray diffraction analysis (XRD) was used to determine the phase composition and structural characteristics of the obtained powders. Peak broadening was observed in the diffraction patterns of the powders subjected to mechanical alloying, indicating a decrease in the crystallite size and an increase in the structural defectiveness. After annealing at a certain temperature, distinct peaks corresponding to the icosahedral phase appeared in the diffraction patterns.
Comparison of XPS and XRD data allowed us to establish a relationship between the elemental composition, chemical state of the surface, and phase composition of powders obtained by mechanical alloying. It was shown that mechanical alloying promotes mixing of components at the atomic level and creates conditions for the formation of an icosahedral phase during subsequent heat treatment.
Author: Shilong Yin, Zhi Xie, Qing Bian, Bo He, Zhiyun Pan, Zhihu Sun, Zheng Wei, Liying Qian, Shiqiang Wei
Institute: College of Life Sciences, Hohai University, Nanjing 210098, P.R. China, National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei 230029, P.R. China, Institute of Science, PLAUST, Nanjing 210007, P.R. China