Shockwave generates < 100 > dislocation loops in bcc iron

Suvranu De,Fei Gao,Huiqiu Deng,Fanjiang Meng,Chenyang Lu,Lumin Wang,Qing Peng,Yizhong Yang

doi:10.1038/s41467-018-07102-3

Abstract

The formation mechanism of < 100 > interstitial dislocation loops in ferritic steels stemming from irradiation remains elusive, as their formations are either too short for experiments, or too long for molecular dynamics simulations. Here, we report on the formation of both interstitial and vacancy dislocation loops in high energy displacement cascades using large-scale molecular dynamics simulations with up to 220 million atoms. Riding the supersonic shockwave generated in the cascade, self-interstitial atoms are punched out to form < 100 > dislocation loops in only a few picoseconds during one single cascade event, which is several orders of magnitude faster than any existing mechanisms. The energy analysis suggests that the formation of the interstitial loops depends on kinetic energy redistribution, where higher incidence energy or larger atom mass could improve the probability of the direct nucleation of interstitial dislocation loops.

Highlights

The formation mechanism of < 100 > interstitial dislocation loops in ferritic steels stemming from irradiation remains elusive, as their formations are either too short for experiments, or too long for molecular dynamics simulations
It has been suggested that the loops can be formed directly from bombardment[8], there is no direct observation of the formations of < 100 > interstitial loops, neither from experiments nor molecular dynamics (MD) simulations in the past half century
We investigate the displacement cascades in pure bcc iron via molecular dynamics simulations at a temperature of 300 K

Summary

Introduction

The formation mechanism of < 100 > interstitial dislocation loops in ferritic steels stemming from irradiation remains elusive, as their formations are either too short for experiments, or too long for molecular dynamics simulations. We report on the formation of both interstitial and vacancy dislocation loops in high energy displacement cascades using largescale molecular dynamics simulations with up to 220 million atoms. Stimulations like stress[22], temperature[9], and impurities (carbon[17], chromium[11], helium[23], etc) could change the relative stability of over clusters, and the rate of reaction or transformation, but not enough to explain their common occurrence of loops under irradiation[17] All these proposed mechanisms require a long time (i.e. nanoseconds and above) due to the high energy barriers. We propose a punch mechanism for the formation of loops by supersonic shockwave during high energy displacement cascade in bcc iron This process occurs very quickly, in only a few picoseconds (ps, 10−12 seconds).

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Conclusion