Positron trapping mechanism in plastically deformed magnesium

Abstract

In order to investigate positron–dislocation interactions, the evolution of the positron lifetime parameters with the degree of deformation of Mg samples was studied. For a low degree of thickness reduction a second component of 244 ps could be decomposed from the positron lifetime spectra. This component was attributed to dislocations introduced during deformation. For thickness reductions higher than 15% the value of the second component increases to 253 ps. This lifetime was assigned to jogs introduced along dislocations when multiple deformation systems were activated at high degrees of deformation. Positron experimental results were interpreted by the assumption that dislocations act as a previous step to positron localization at jogs. A trapping model with three stages, bulk annihilation and trapping at both dislocations and jogs, has been proposed to describe the trapping mechanism in the highly deformed samples. A sample with a thickness reduction of 40% was annealed from room temperature to 525 K. A recovery stage centred at 425 K was been detected. According to the literature this stage has been assigned to anneal out of dislocations.

Keywords:

• positron annihilation
• positron defect
• dislocation

Acknowledgements

This work has been supported by Ministerio de Ciencia e Innovación of Spain, project (FIS2007-61326)