Irradiation-Driven Recrystallization in Fusion-Grade Tungsten: A Mesoscale, Microstructure-Aware Model

TL;DR

This work tackles irradiation-driven recrystallization in fusion-grade tungsten by developing a three-way coupled framework that integrates CPFE, stochastic cluster dynamics, and vertex dynamics to capture the co-evolution of plastic deformation, irradiation damage, and grain-boundary motion on realistic microstructures. The method reveals that RX kinetics are exponentially sensitive to temperature via thermally activated GB mobility, while rhenium produced by neutron transmutation can markedly slow GB motion and raise the effective RX temperature. Under fusion-relevant irradiation, the model predicts a substantial reduction of the recrystallization temperature relative to unirradiated microstructures, with Re segregation partially offsetting this effect and potentially restoring or elevating the RX limit. Avrami-like kinetics with an exponent near unity emerge, indicating growth perpendicular to grain boundaries dominates RX; the final recrystallized state shows softening in mechanical response. Collectively, the framework provides a predictive tool to assess lifetime, operating envelopes, and alloy-design strategies for W-based plasma-facing materials in fusion environments, enabling simultaneous consideration of temperature, irradiation, and microstructural features.

Abstract

Tungsten (W) is the leading candidate material for plasma-facing components in fusion reactors, yet its upper operational temperature is limited by premature grain growth and recrystallization processes. Irradiation adds further complications by generating defect clusters and transmutation products that alter both the driving forces and kinetics of grain boundary motion. In this work, we develop a physics-based, multiscale framework that couples crystal plasticity, stochastic cluster dynamics, and discrete grain boundary dynamics to model the co-evolution of plastic deformation, irradiation damage, and grain growth in fusion-grade tungsten polycrystals. The approach enables simulations on realistic microstructures with arbitrary grain size and misorientation distributions, without recourse to mean-field simplifications. The model captures (i) the spatial heterogeneity of dislocation density distribution during hot working; (ii) irradiation-induced defect accumulation under fusion conditions, and (iii) the buildup of chemical and elastic driving forces for grain boundary migration and microstructural evolution. Parametric studies demonstrate the dominant influence that temperature has on thermally activated grain-boundary mobility, a weaker dependence on prior strain, and a pronounced retardation of recrystallization by rhenium segregation arising from neutron transmutation. Under fusion energy irradiation conditions, our framework predicts a substantial reduction of the effective recrystallization temperature relative to unirradiated microstructures, while Re production restores and even elevates this limit. By providing quantitative projections of recrystallization kinetics and in-service recrystallization temperatures, this work establishes a predictive tool for assessing the lifetime and operational envelope of W-based plasma-facing materials under fusion conditions.

Figures (14)

• Figure 1: Misorientation dependence of the GB energy, $\gamma(\theta)$, and denuded zone width, $\lambda(\theta)$.
• Figure 2: Schematic flowchart illustrating the coupling vertex dynamics, stochastic cluster dynamics and crystal plasticity.
• Figure 3: Microstructural details of the polycrystal considered in this work. The left figure shows a cross-sectional view of the as-processed material obtained via scanning electron microscopy. Superimposed is the histogram of grain sizes. The dashed box indicates a cutout of a subspecimen similar to that used in the simulations. The right figure shows a reconstruction from EBSD analysis of the polycrystal employed in the simulations. The grain orientation of the material is colored according to the referential standard triangle shown in the inset. The arrows indicate the direction of loading in the CPFE simulations.
• Figure 4: Microstructural details of the polycrystalline specimen considered in the simulations. \ref{['fig:misorientation']} Spatial grain boundary misorientation map. \ref{['fig:grainSizeDistribution']} Grain size distribution.
• Figure 5: \ref{['fig:cpdf']} Cumulative PKA energy probability distribution function for neutron irradiation of W in the equatorial plane of the first wall armor structure in DEMO-hcll marian2025computational. The average energy of the distribution is 5.9 keV. The distribution for HFIR irradiations (fission neutrons) ZHANG2023101443 is added for comparison \ref{['fig:ReConcentration']} Transmutation rate of W into Re as a function of irradiation dose (from ref. gilbert2013neutron). The graph stops at the accumulated dose after 1 year of continuous reactor operation.