Energetics of vacancy segregation to [100] symmetric tilt grain boundaries in bcc tungsten

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.

Interaction of radiation-induced defects with tungsten grain boundaries at across scales: a short review

“…To show whether the defects near the GB have a thermodynamic tendency to segregate to the GB (processes 4/4′ and 5/5′ in Fig. 1), researchers conducted molecular statics (MS) calculations of energetic properties of the V/SIA in a certain range of the GB at 0 K [20,[22][23][24][25][26][27][28]. To do this, one removes or inserts an atom near the GB, and then relaxes the GB structure using an energy-minimization method, e.g.…”

“…Extensive theoretical efforts were made to understand the radiation performance of NC W in terms of the defect production [14,[17][18][19][20][21] and energetic and kinetic interactions with GBs of the defects [14,17,20,[22][23][24][25][26][27][28][29]. In this paper, the theoretical advances in the across-scale selfhealing mechanisms for the radiation damage in NC W are reviewed.…”

“…Figure 1 illustrates the possible three interaction types of radiation with GBs in W (types I, II, III). Although a complete interplay picture involves the defect behavior not only near the GB [14,[17][18][19][20][21][22][23][24][25][26][27][28][29] but also in the bulk [30][31][32][33][34] or near the surface [35][36][37][38], the focus in the present paper is on the former one. Type I is relevant to defect production near the GB [14,[17][18][19][20][21].…”

“…The cascade could also directly affect the GB's structure, energy and mobility. Type II is related to the defect behavior near the GB [14,20,[22][23][24][25][26][27][28]. The stable defects formed after the annealing of the cascade interact with the GB via complex processes of segregation, annihilation, clustering, diffusion, dissociation, and emission from the GB.…”

“…Researchers proposed several self-healing mechanisms involving individual or multiple parts of these processes in W [14,20,[22][23][24][25][26][27][28]. These mechanisms include GB-accelerated V/ SIA migration and SIA-V recombination [14,20,[22][23][24][25][26][27][28], interstitial-emission (IE) induced annihilation [24,27,28], coupling of the V approaching to the GB with the interstitial motion within the GB (CVI) [27], and interstitial reflection (IR) by the locally dense GB region [27]. In addition, the defects trapped at the GB also modify the GB's kinetics (type III), leading to other self-healing mechanisms, such as the GB-motion induced trapping of bulk V-clusters [29].…”