Application of Positron Annihilation to Metallic Alloys
Segregation of impurity atoms to or depletion from surfaces or grain boundaries plays a significant role in the mechanical and corrosion resistance of metallic materials. A great deal of effort has been spent on detecting the extremely thin layers of impurity enrichment or depletion at those boundaries by suitable analytical techniques on open or freshly broken intergranular surfaces, this volume containing many references. It is the purpose of this paper to show that not only such more open and extended structures like surfaces or grain boundaries but also holes on an atomic scale like single vacancies attract or reject impurity atoms and that their behavior at these local sites is very similar. Since the number of vacancies which are generated in solids in thermal equilibrium is relatively small, the study of the phenomena of impurity-vacancy interaction requires a technique, which is extremely sensitive to and somewhat specific for vacancies, the positron annihilation. After introducing two possible techniques to utilize this effect, the positron lifetime measurements and the Doppler-shift of the annihilation radiation, data will be presented for the study of thermal vacancy formation in pure metals and particularly some noble metal alloys.
KeywordsImpurity Atom Pure Copper Positron Annihilation Metallic Alloy Formation Enthalpy
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