Abstract
The harsh irradiation environment poses serious threat to the structural integrity of leading candidate for plasma-facing materials, tungsten (W), in future nuclear fusion reactors. It is thus essential to understand the radiation-induced segregation of native defects and impurities to defect sinks, such as grain boundaries (GBs), by quantifying the segregation energetics. In this work, molecular statics simulations of a range of equilibrium and metastable [100] symmetric tilt GBs are carried out to explore the energetics of vacancy segregation. We show that the low-angle GBs have larger absorption length scales over their high-angle counterparts. Vacancy sites that are energetically unfavorable for segregation are found in all GBs. The magnitudes of minimum segregation energies for the equilibrium GBs vary from −2.61 eV to −0.76 eV depending on the GB character, while those for the metastable GB states tend to be much lower. The significance of vacancy delocalization in decreasing the vacancy segregation energies and facilitating GB migration has been discussed. Metrics such as GB energy and local stress are used to interpret the simulation results, and correlations between them have been established. This study contributes to the possible application of polycrystalline W under irradiation in advanced nuclear fusion reactors.
Highlights
The harsh irradiation environment poses serious threat to the structural integrity of leading candidate for plasma-facing materials, tungsten (W), in future nuclear fusion reactors
We have carried out molecular statics simulations to explore the energy landscapes of vacancy segregation to a range of equilibrium and metastable [100] symmetric tilt grain boundaries (STGBs) in bcc tungsten (W)
(1) For the equilibrium GBs, the magnitudes of minimum vacancy segregation energies vary from −2.61 to −0.76 eV, while those of mean vacancy segregation and absorption length scales range from −1.01 to −0.44 eV and from 3.18 to 12.41 Å, respectively, depending on the GB character
Summary
The harsh irradiation environment poses serious threat to the structural integrity of leading candidate for plasma-facing materials, tungsten (W), in future nuclear fusion reactors. A quantitative picture of defect segregation energetics is essential to the understanding of dynamic processes of defect evolution in materials under irradiation On this very topic, density functional theory calculations[20,21] and atomistic simulations[9,10,11,22,23,24,25,26,27,28,29] have been frequently used to describe the segregation energetics of point defects (including impurities) to a series of GBs. For example, Tschopp, Solanki and coworkers have performed extensive atomistic simulations to investigate the effects of GB character on the formation energetics of point defects, such as vacancy[9,22,23,24,30], self-interstitial[9], hydrogen[25,26], helium[26,27], carbon[26,28] and various other impurities[23,26]. The objective of this work is to gain further understanding on these key issues based on atomistic simulations using an embedded atom method (EAM) potential, and possibly provide inputs of energetics and vacancy absorption length scales for modelling and simulation of W at larger scales
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