The study of the phase composition and microstructure of quasicrystalline alloys of the Al-Cu-Fe-Si system, especially those close to the eutectic point, is of considerable interest for materials science. These alloys, which have a unique combination of physical and mechanical properties, are used in various fields of technology. This paper presents the results of a study of a new phase found in Al-Cu-Fe-Si alloys, characterized by a tetragonal crystal structure derived from the silicon structure, with a chemical composition close to Al3Si7.
Experimental studies were conducted using X-ray diffraction, scanning electron microscopy and energy-dispersive analysis. Analysis of diffraction patterns showed the presence of reflections that do not correspond to known phases in the Al-Cu-Fe-Si system. Further decoding of the structure allowed us to establish a tetragonal syngony with lattice parameters close to the modified silicon structure. Microscopic studies revealed that the new phase is formed in the form of dendritic inclusions distributed in the main matrix consisting of the aluminum phase and other intermetallic compounds.
Energy dispersive analysis confirmed the presence of aluminum and silicon in the new phase in a ratio close to Al3Si7. It is assumed that the stabilization of the tetragonal structure of silicon in this phase is due to the interaction with aluminum atoms and, possibly, an insignificant entry of copper and iron atoms into the crystal lattice. The formation of this phase can have a significant effect on the mechanical properties of alloys, in particular, their strength and ductility. Further studies are aimed at studying the thermal stability of the new phase and its effect on the crystallization processes of Al-Cu-Fe-Si alloys.
. The study revealed the presence of a eutectic structure in the Al-Cu-Fe-Si system consisting of tetragonal Al single crystals and quasicrystals obtained by vacuum casting. It was experimentally confirmed that the addition of silicon effectively stabilizes the face-centered icosahedral (FCI) phase. The stability region of the FCI phase in the pseudo-ternary diagram of Al-Cu-Fe-(Si) corresponds to the compositional constraints dictated by the Hume-Rothery rules for electron concentrations. It was shown that the FCI phase is formed as the main phase upon substitution of 7 at.% Si:Cu/Fe. This discovery opens up possibilities for crystallization of the FCI phase by arc melting.
A series of quaternary aluminum alloys with the addition of Si7, which form orthorhombic CuAl2 dendrites and individual needles of the hexagonal intermetallic Al-Fe-Si, have been synthesized. The stability of the Al3Si phase, previously predicted by ab-initio theoretical calculations, has been experimentally confirmed for the first time. The overall Vickers hardness of the studied alloys remained virtually unchanged at a Si concentration of up to 7 at.%. Alloying with 10 at.% Si:Fe or Si:Cu resulted in a decrease in hardness by 330 HV1, which is 43% compared to the base alloy without alloying. This is explained by the formation of a eutectic with low hardness.
Author: Piotr Joseph Bardzinski
Institute:
Faculty of Chemistry, University of Wroclaw, ul. F. Joliot-Curie 14, 50-383 Wroclaw, Poland (current location)
Faculty of Mining and Geodesy, Wroclaw University of Science and Technology, ul. Na Grobla 15, 50-421, Wroclaw, Poland (former name)