Dislocations and plastic deformation of quasicrystals

The results of experimental studies on the plastic mechanical behavior of single-quasicrystals of Al-Pd-Mn at temperatures between 680 and 800 °C are reviewed. The stress-strain curves are characterized by a pronounced yield drop followed by a continuous decrease of the flow stress with increasing strain. The analysis of the microstructure of the deformed material and in-situ straining experiments in the electron microscope show that plastic deformation is based on a dislocation mechanism. The glide geometry of the dislocations can be derived from experiments in which the six-dimensional Burgers vectors and the glide planes are determined. Measurements of the thermodynamic deformation parameters, in particular, the activation volume and the activation enthalpy, indicate that dislocation motion is thermally activated and controlled by localized obstacles. These obstacles can be provided by Mackay-type clusters which form the basic structural elements according to current structure models of icosahedral Al-Pd-Mn. The decrease of the flow stress with increasing strain is explained as deformation softening caused by destraction of the structural and chemical order of the material by the motion of dislocations.