Characterisation of atomic-scale defects in ODS ferritic alloys by positron annihilation

ABSTRACT

The vacancy-type defects and their local chemical environment in different ODS alloys produced in the USA (14YWT), China (K5) and Russia (ODS EP-450) are studied. The Angular Correlation of Annihilation Radiation (ACAR), which is one of the positron annihilation spectroscopy method, was used. It was shown that in all alloys, except 14YWT, the dominant type of positron traps are vacancy-like defects, localised in matrix or associated with dislocations and/or interfaces of the incoherent particles. In the case of 14YWT alloy, which contains Y–Ti–O nanoclusters of a high density, the positrons confine and annihilate at O-vacancy pairs or complexes within nanoclusters. It is testified by enhanced electron density in annihilation sites and neighbourhood of Ti and Y atoms. These results, obtained by the ACAR method, indicate that the vacancies play an essential role in the formation of nanoclusters in ODS 14YWT alloy as it was theoretical predicted by first-principle calculations.

KEYWORDS:

• ODS alloys
• Y–Ti–O nanoclusters
• vacancy-like defects
• positron annihilation spectroscopy

Acknowledgements

We thank Dr. D.T. Hoelzer at ORNL for providing the 14YWT and 14WT samples for this study. The research was carried out within the state assignment of FASO of Russia (theme ‘Spin’, No. АААА-А18-118020290104-2).

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

A. P. Druzhkov http://orcid.org/0000-0001-9586-9072

D. A. Perminov http://orcid.org/0000-0003-1384-6446