Intermetallic alloys of the Al-Cu-Fe system containing quasicrystalline phases are of considerable interest due to their unique combination of properties, such as high hardness, wear resistance, and low friction coefficient. However, their brittleness limits their practical application. A detailed study of the properties of both quasicrystalline and crystalline phases present in the microstructure is critical to understanding and improving the mechanical properties of these alloys.
The mechanical properties of quasicrystals, in particular AlCuFe, are determined by their aperiodic structure. The absence of periodicity hinders the movement of dislocations, the main mechanism of plastic deformation in crystalline materials. As a result, quasicrystals usually exhibit high hardness and brittleness at room temperature. At elevated temperatures, dislocation activity is possible, leading to some increase in plasticity.
The mechanical properties of icosahedral AlCuFe quasicrystals were studied and compared with the corresponding parameters of crystalline intermetallics using the indentation and three-point bending methods. Quasicrystal phases are characterized by significant hardness (approximately 1000 HV) and pronounced elastic deformation (H/E > 0.08), but demonstrate low fracture toughness, which leads to unstable fracture.
The introduction of icosahedral particles into the crystalline matrices of Al2Cu or AlFe helps to increase the resistance to the propagation of subcritical cracks. Unlike the fracture along certain planes in crystalline Al13Fe4, icosahedral quasicrystals are characterized by an uneven fracture surface.
Evidence of plastic deformation has been found in quasicrystals. A discussion is presented regarding the mechanism underlying this deformation.
Crystalline phases such as Al2Cu or FeAl present in Al-Cu-Fe alloys can have a significant effect on the overall mechanical properties of the material. The mechanical properties of these phases depend on their crystal structure, grain size and morphology. The introduction of finely dispersed strengthening crystalline phases can increase the strength and ductility of the composite material.
Changing the ratio of quasicrystalline and crystalline phases, as well as controlling the size and distribution of phases, allows optimizing the mechanical properties of Al-Cu-Fe alloys. Thermomechanical processing methods such as quenching and tempering affect the phase composition and microstructure, and thus the mechanical properties of the material. Further research aimed at developing more complex technological processes is necessary to improve the ductility of quasicrystalline alloys and expand their areas of application.
Author: U Köster, W Liu, H Liebertz, M Michel
Institute: Department of Chemical Engineering, University of Dortmund, W-4600 Dortmund 50, Germany