Nano-sized prismatic vacancy dislocation loops and vacancy clusters in tungsten

Jan Fikar,Robin Schäublin,Daniel R Mason,Duc Nguyen-Manh

doi:10.1016/j.nme.2018.06.011

Abstract

The vacancies produced in high energy collision cascades of irradiated tungsten can form vacancy clusters or prismatic vacancy dislocation loops. Moreover, vacancy loops can easily transform into planar vacancy clusters. We investigated the formation energies of these three types of vacancy defects as a function of the number of vacancies using three embedded-atom method tungsten potentials. The most favorable defect type and vacancy loop stability was determined. For very small sizes the planar vacancy cluster is more favorable than a vacancy loop, which is unstable. The void is the most stable vacancy defect up to quite large size, after that vacancy dislocation loop is more favorable. We conclude that the vacancy dislocation loops are nevertheless hlmetastable at low temperatures as the transformation to voids would need high temperature, in contrast to previous works, which found planar vacancy clusters to have lower energy than vacancy dislocation loops.

Highlights

During high energy irradiation, lattice defects are produced in the form of interstitial- and vacancy- type point defects and clusters
The formation energies divided by the number of defects Ef/N of the vacancy clusters and dislocation loops are reported in Figs. 2–4 for the potentials AT, M4 and Manh and Becquart (MNB), respectively
Our spherical void shape allows us to calculate a more precise average free surface energy γa, which is for the MNB potential very close to the experimental value, see Table 1

Summary

Introduction

Lattice defects are produced in the form of interstitial- and vacancy- type point defects and clusters. Recent simulations [1,2] and experiments [3,4] have shown that nanoscale loops, visible in transmission electron microscope (TEM), can be generated within the heat spike of a displacement cascade. The majority of these point defects mutually annihilates in the cascade cool down phase. While the surviving interstitials tend to form exclusively small prismatic interstitial dislocation loops, the surviving vacancies have more possibilities They can create prismatic dislocation loops or vacancy clusters. We focus on tungsten, one of the prime candidate materials for future fusion reactor designs

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Results

Conclusion