MOLECULAR DYNAMICS SIMULATION OF INITIAL RADIATION DAMAGE IN TUNGSTEN
Man YAO1(),Wei CUI1,Xudong WANG1,Haixuan XU2,S R PHILLPOT3
1 School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024
2 Department of Materials Science and Engineering, University of Tennessee, Knoxiville, TN37996, USA
3 Department of Materials Science and Engineering, University of Florida, Gainesville, FL 32611, USA
Cite this article:
Man YAO, Wei CUI, Xudong WANG, Haixuan XU, S R PHILLPOT. MOLECULAR DYNAMICS SIMULATION OF INITIAL RADIATION DAMAGE IN TUNGSTEN. Acta Metall Sin, 2015, 51(6): 724-732.
Tungsten is a candidate material for the first wall and divertor in a tokamak fusion reactor, in which it is required to withstand a high neutron irradiation. The defects created in cascade form the primary state of damage and their subsequent evolution gives rise to important changes in their microstructures and engineering properties. However, the evolution and aggregation of radiation-induced defects in atomic level can not be observed by experiments up till now. In this work, molecular dynamics (MD) method was used to explore the microstructural processes and atomic mechanism of the formation and evolution of defects in the initial stage of radiation in bcc-W. The range of primary knock-on atom (PKA) energies is 1.0~25.0 keV, and simulation temperature range from 100 to 900 K. The number and distribution of defects produced by displacement cascades have been studied; the influence of PKA direction and temperature on the number of steady Frenkel pairs has also been researched; defect clusters and the threshold energy have been simulated. The results showed that for morphology distribution of defects induced in the peak time of cascade, the more intensive the defects are, the less the steady Frenkel pairs numbers are, on the contrary, the more decentralized the defects are, the more the steady Frenkel pairs numbers are; the number of steady Frenkel pairs is insensitive to PKA direction, but has a trend to decline with the temperature elevating; the percentage of interstitial clusters is higher than that of the vacancy clusters, while vacancies tend to form larger clusters; the average threshold energy of W is less affected by temperature and has certain anisotropy. The results of this work can provide data for analyzing the behavior of W material under nuclear environment.
Fig.1 Evolution curves of number of Frenkel pairs with time in displacement cascade casued by a set of primary knock-on atoms (PKAs) with various energies at 100 K
Fig.2 Distributions of radiation-induced Frenkel pairs in different moments at 100 K (The PKA energy is 10.0 keV and the PKA velocity direction is parallel to the crystallographic direction [135] of bcc-W, black balls represent the vacancies and white balls the interstitials)
Fig.3 Distributions of radiation-induced Frenkel pairs at peak time in different morphologies at 100 K (The PKA energy is 20.0 keV, the PKA velocity direction is parallel to the crystallographic direction [135] of bcc-W, and in the circles the alternating sequence of interstitials and vacancies are shown)
Fig.4 Numbers of survival Frenkel pairs at steady stage as a function of PKA energy (Solid dots represent the numbers of steady Frenkel pairs estimated by Norgett-Robinson-Torrens (NRT) formula NFS(NRT), the hollow circles are the values simulated by molecular dynamics (MD) NFS, the bars represent the standard deviations)
Fig.5 Cascade efficiency h as a function of PKA energy
PKA direction
NFS
F
[100]
7.00±0.02
-4.4%
[110]
6.90±0.22
-5.8%
[111]
6.67±0.02
-8.9%
[112]
7.97±0.04
8.9%
[135]
8.07±0.14
10.2%
Table1 Number and its floating of Frenkel pairs at steady stage along various crystallographic directions of bcc-W with PKA energy of 3.0 keV at 100 K
Fig.6 NFS at steady stage in cascade simulations with PKA energies of 3.0 keV (a) and 5.0~15.0 keV (b) at various temperatures 100~900 K of bcc-W
Fig.7 Fractions of interstitials fcli and vacancies fclv via PKA energy (10.0~25.0 keV) at 100 K at steady stage
Fig.8 Evolution of point defects during steady stage at 900 K with PKA energy 15.0 keV at 20.52 ps (a), 25.90 ps (b), 28.83 ps (c), 31.76 ps (d), 34.70 ps (e) and 40.72 ps (f) (Black balls represent the vacancies and white balls the interstitials)
Fig.9 Relationship of cluster size (the number of defects in each cluster) and number with PKA energy 25.0 keV at 100 K
Fig.10 Comparisons of threshold energies simulated in this work and other works via simulations or experiments for W
Fig.11 Threshold energy at 100 K along different crystallographic directions (Blue dots represent average value and red dots represent the values with the frequency of maximum)
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