Studying the mechanisms of plastic deformation of quasicrystals (QC) at high temperatures is an important task in materials science. Unlike conventional crystals, QCs have an aperiodic structure with long-range order, which leads to unique mechanical properties. High-temperature plastic deformation of QCs, in particular the icosahedral phases of Al–Cu–Fe and Al–Pd–Mn, is a complex process in which dislocations play a key role.
In QC, dislocations differ from those in normal crystals. They are characterized by the presence of a Burgers vector, which is not a lattice vector. Dislocations in QC can be either perfect or incomplete (partial). The motion of dislocations in QC is hindered by the aperiodic structure, which leads to high flow stresses.
Microstructure analysis of hot-deformed icosahedral quasicrystals (IQC) Al62.5Cu25Fe12.5 and Al70.4Pd21.2Mn8.4 was performed using transmission electron microscopy (TEM). High-density dislocations and characteristic deformation contrasts were revealed for the first time in Al–Cu–Fe IQC. This observation serves as an argument in favor of the fact that dislocation movement plays a key role in the deformation process of Al–Cu–Fe IQC.
In quasicrystalline materials, dislocation motion leads to the formation of phonon configurations. TEM studies demonstrate that these phonon structures are subject to disappearance due to enhanced diffusion at elevated temperatures.
High-temperature plastic deformation of icosahedral Al–Cu–Fe and Al–Pd–Mn QCs occurs through several mechanisms, including:
Dislocation slip: Dislocations move along specific slip planes under the action of applied stress.
Dislocation climb: Dislocations can overcome obstacles by climb, which is a thermally activated process.
Double cross slip: Dislocations can change slip plane by double cross slip, which helps to increase plasticity.
Temperature and strain rate have a significant effect on the mechanisms of plastic deformation QC. As the temperature increases, the mobility of dislocations increases, which leads to a decrease in the flow stress. As the strain rate increases, the flow stress increases, and the contribution of dislocation climb decreases.
Dislocation mechanisms play an important role in the high-temperature plastic deformation of icosahedral Al–Cu–Fe and Al–Pd–Mn QCs. Understanding these mechanisms allows the development of new materials with improved mechanical properties for high-temperature applications.
Author: Renhui Wang, Wenge Yang, Jianian Gui, Knut Urban
Institute: Department of Physics, Wuhan University, Wuhan, 430072, China, Institute of Solid State Physics, Research Center Juelich GmbH, D-52425 Juelich, Germany