Tungsten (W) is a leading candidate material for plasma-facing components in future fusion reactors, such as ITER, where it will be subjected to extreme neutron irradiation. Understanding the relationship between irradiation-induced microstructural changes and mechanical property degradation is critical to component performance and lifetime prediction. While the behaviours of neutron irradiation on tungsten has been examined, a complete picture of the evolution of different defect populations (dislocation loops vs. nanovoids) and their collective effect on radiation-induced hardening at different ITER-relevant temperatures is still lacking. This lack of knowledge is a drawback to the development of truly radiation-resistant tungsten microstructures. This study examines the microstructure and hardening response of two ITR-grade pure tungsten materials after neutron irradiation to a dose of ~1 dpa at two different temperatures (600 °C and 1000 °C). The evolution in defect morphology, density, and size was quantitatively characterized using transmission electron microscopy (TEM). The contribution of these defects to hardening was evaluated using the Dispersed Barrier Model (DBM), and several superposition rules were tested to achieve good agreement with the total hardening effect. Irradiation caused the formation of two main defect types in both grades: dislocation loops and nanovoids, whereas the general grain and subgrain structure remained stable. At the higher irradiation temperature of 1000 °C, the defect number density decreased, and the average defect size increased compared to 600 °C. Critically, nanovoids had higher thermal stability than the dislocation loops. Analysis using the DBM showed that hardening due to voids was more important than that due to loops at all irradiation temperatures. The squared-sum rule with a size-dependent barrier-strength coefficient provided the best fit for the combined hardening effect. Nanovoids were found to be the prevailing type of hardening at higher irradiation temperatures (1000 °C). This finding provides proof of principle that void evolution, rather than dislocation-loop behavior, is the controlling parameter for the mechanical-property degradation of tungsten under fusion-relevant conditions. The results highlight the crucial importance of advanced microstructural design approaches (in particular those focused on improving void swelling resistance and engineering effective defect sinks) for the development of radiation-resistant tungsten for advanced fusion reactor applications.
Wang et al. (Wed,) studied this question.