Interaction Between Interstitial Dislocation Loop and Micro-Crack in bcc Iron Investigated by Molecular Dynamics Method
LIANG Jinjie1,2, GAO Ning2,3, LI Yuhong1()
1 School of Nuclear Science and Technology, Lanzhou University, Lanzhou 730000, China 2 Institute of Modern Physics, Chinese Academy of Sciences, Lanzhou 730000, China 3 Key Laboratory of Particle Physics and Particle Irradiation, Ministry of Education, Institute of Frontier and Interdisciplinary Science，Shandong University, Qingdao, Qingdao 266237, China
Cite this article:
LIANG Jinjie, GAO Ning, LI Yuhong. Interaction Between Interstitial Dislocation Loop and Micro-Crack in bcc Iron Investigated by Molecular Dynamics Method. Acta Metall Sin, 2020, 56(9): 1286-1294.
In fission or fusion nuclear reactors, the interaction between the high energy particles (e.g. neutrons) and atoms would result in the radiation damages in materials, affecting the performance of materials and lifetime of reactors. The radiation hardening, embrittlement, swelling, creep, fatigue and so on are all related with the radiation damages in materials. Therefore, it is necessary to understand the underlying physics for developing the radiation resistant materials in future. Until now, the displacement cascade process has been studied for decades through computer simulation method. The other properties listed above have also been focused by different groups. However, in addition to these properties, it is also important to understand the degradation of mechanical properties induced by the supersaturated point defects and their clusters, especially the contribution from the interaction between dislocations and radiation defects. Under irradiation, in addition to the self-interstitial dislocation loops formed by the clustering of the self-interstitial atoms, the micro-crack can also be formed in bulk and near the surface of the materials, related with the gas bubble, grain boundary and blister, which would seriously influence the application of materials used in nuclear power plants. Under irradiation, in addition to the normal crack expansion under the effect of stress, these cracks would be key factors to irradiation assistant stress corrosion crack (IASCC) phenomena, which have been studied for decades. In previous studies, although the properties of self-interstitial dislocation loops and micro-crack have been studied independently, the interaction between them under the condition of irradiation has not been fully studied. In this work, the detailed interactions between self-interstitial dislocation loop and micro-crack in bcc iron have been studied at atomic scale with molecular dynamics (MD) simulation method. The results indicate that the relative position between them, the slope of micro-crack, the size of loop and existence of free surface, would all affect the interaction between loop and micro-crack and the related finally micro-structure after the interaction. Under different conditions, the interactions either induce the formation of micro-scale complex radiation damage structure, or the absorption of dislocation by micro-crack, resulting in the rugged crack tips, which would affect the growth and expansion of micro-crack, the degradation of mechanical properties of materials under irradiation. Furthermore, the results can also compare with the formation of dislocation and dislocation loop free zone near the crack tip observed experimentally, providing new understanding to these phenomena. Therefore, all these results provide new possible understandings of radiation damages.
Fund: National Magnetic Confinement Fusion Energy Research and Development Program of China(2018YFE0308101);National Natural Science Foundation of China(11675230);National Natural Science Foundation of China(11775102);Youth Innovation Promotion Association, Chinese Academy of Sciences(2016366)
Fig.1 Schematics of interaction between the interstitial dislocation loop and micro-crack (l—distance between dislocation loop and crack tip in Y direction, R—radius of dislocation loop, d—distance between dislocation loop and crack tip in X direction, P—the position of the crack tip, k—slope of crack, 2θ—crack tip opening angle)(a) crack is inside of the material(b) crack is from the free surface of material
Fig.2 Evolutions of the system with the interaction between the dislocation loop and micro-crack with d=1.5 nm, k=0.05 and R=1.5 nm
Fig.3 Evolutions of the system with the interaction between the dislocation loop and micro-crack with d=3.2 nm, k=0.05 and R=1.5 nm
Fig.4 Evolutions of the system with the interaction between the dislocation loop and micro-crack with d=4.5 nm, k=0.05 and R=1.5 nm(a) formation of 1/2[] dislocation segment after the conjugate gradient method relaxation (b~e) molecular dynamics simulation results at 300 K under 0 Pa pressure with time up to 1.8×10-11 s, 3×10-11 s, 3.09×10-11 and 3.12×10-11 s, respectively (The movements of dislocation loop and 1/2[] dislocation segment along their Burgers vectors are shown in Figs.4b and c, respectively. The interactions between them are shown in Figs.4d and e)
Fig.5 Evolutions of the system with the interaction between the dislocation loop and micro-crack with d=1.5 nm, R=1.5 nm and k=0.10
Fig.6 Evolutions of the system with the interaction between the dislocation loop and micro-crack with d=1.5 nm, R=1.5 nm and k=0.15
Fig.7 Evolutions of the system with the interaction between the dislocation loop and micro-crack with d=1.5 nm, R=1.5 nm and k≥0.20
Fig.8 Evolutions of dislocation loop and micro-crack with the repulsive interaction between them with d=3.2 nm, R=1.5 nm and k=0.10 (The distance between them increases with simulation time (t))(a) t=1.5×10-12 s(b) t=4.8×10-12 s(c) t=7.5×10-11 s
k
R=1.5 nm
R=2.0 nm
R=3.0 nm
Inside of bulk
Free surface
Inside of bulk
Free surface
Inside of bulk
Free surface
0.05
11.7
11.4
11.4
12.3
14.7
24.3
0.10
25.2
16.5
Unabsorbed
16.2
Unabsorbed
21.6
0.15
12.6
12.6
15.9
14.7
Unabsorbed
18.9
0.20
10.5
9.9
17.7
15.0
Unabsorbed
15.6
0.25
8.1
7.5
10.5
10.5
14.4
17.7
Table 1 The simulation time for dislocation loop to be fully absorbed by micro-crack with and without the effect of free surface with d=15 nm under the condition of different R and k(10-3 ns)
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