Positron annihilation in deformed crystals

Dislocations and their density control the mechanical properties of metals, like ductility and hardness. Different techniques can be used to study the distribution, arrangement and density of dislocations. Microscopic methods like the transmission electron microscopy or the counting of etch pits are limited to low dislocation density and require very elaborate sample preparation. So methods based on the scattering of particles or waves at dislocations become increasingly promising. This work presents a systematic study of different scattering methods to measure dislocation densities in deformed copper single and polycrystals and in copper-gold alloys. Measurements of the electrical resistance are able to determine the dislocation density in high purity metals. In alloys the deviation from the Matthiessen's rule impedes the determination of dislocation densities. In this work the positron annihilation spectroscopy and the X-ray Bragg profile analysis are studied as alternative methods, especially for alloys. The results from the electrical measurements can then be independently checked. It is shown that positrons are a very suitable method to determine the type of the crystal defects, but dislocation densities can only be measured in copper single crystals in a small range. In copper polycrystals the dislocation densities can not be determined by positrons due to the high detrapping rate of positrons. X-ray Bragg profile analysis is an advantageous method to determine the dislocation density in pure metals and alloys. Point defects do not influence the precision of this method. Thus a combination of the X-ray and the positron method is able to reveal influences of vacancies and their agglomerates on the electrical resistance which have to be allowed for any determination of dislocation density. In addition models for the deviation from Matthiessen's rule can be tested. (author)