Microstructure evolution during electron and ion irradiation in commercial purity magnesium

Abstract

Microstructure evolution during in situ electron irradiation at room temperature within the transmission electron microscope has been studied on commercial purity magnesium. Magnesium foils of purity 99.8% were examined for comparative studies of defect structure formed by 200 keV electrons and 1 MeV krypton ions. Transmission electron microscopy has been used to quantify the type and nature of the microstructural changes taking place during irradiation. Hexagonal-shaped faulted c-component dislocation loops with Burgers vector of are formed by electron irradiation. Formation of inner un-faulted loops also takes place inside the faulted loops. Analysis shows that all the faulted c-component dislocation loops are interstitial in nature and growth rate of these loops is proportional to the irradiation time. Dislocation loops with Burgers vector also form but most of these loops shrink and disappear during subsequent electron irradiation. In some of the foils, only the pre-existing dislocations in the microstructure were observed to transform into vacancy type loops and helical configurations and no other irradiation damage appeared. Ion irradiation for a dose up to 0.1 dpa produced dislocation loops with Burgers vector of and these loops were mixed vacancy and interstitial in character.

Keywords:

• TEM
• ion irradiation
• dislocations

Acknowledgements

This work is sponsored by NSERC, UNENE (COG, OPG) and Nu-Tech Precision Metals under the Industrial Research Chair Program in Nuclear Materials at Queen’s University. The ion irradiation was accomplished at the Electron Microscopy Centre for Materials Research at Argonne National Laboratory, a US Department of Energy Office of Science Laboratory [Contract Number DE-AC02-06CH11357] by UChicago Argonne, LLC. The authors are grateful to Dr. Mark Kirk and Pete Boldo of Argonne National Lab for their help on the ion beam facility. Authors are also thankful to Prof. Chunghao Woo, Hong Kong Polytechnic University and Malcolm Griffiths, Chalk River Laboratories for their helpful comments.