In a fusion environment, tungsten, a plasma-facing material in a reactor, is subject to the irradiation of high-energy neutrons, generating a large amount of displacement damage and transmutation products (such as rhenium, Re). We studied the evolution of defects under irradiation in W and W-Re systems using the density functional theory (DFT) and rate theory (RT) method. The results indicate that the evolution of irradiation defects is mainly affected by the irradiation dose, dose rate, and temperature. During irradiation, loops form first in W, followed by the generation of voids, which are due to the different migration energies of point defects. Higher dose rates result in a higher density and larger size of defects in tungsten. Higher temperatures cause a decrease in void density and an increase in size. The results obtained at 600 °C were in good agreement with the reported TEM data. In W-Re alloys, it is indicated that the formation of loops is delayed because Re suppresses the nucleation of loops. The dynamic introduction of Re in W stabilizes the growth of defects compared to W-Re alloys, suggesting that transmuting elements have less detrimental effects on irradiation than alloying. As defect densities and sizes were quantified under different irradiation conditions, the results provide data for the multi-scale simulation of the radiation damage and thermal/mechanical properties in plasma-facing materials under fusion conditions.

The structural evolution of Cr-coated Zr-4 after irradiation was studied via in situ TEM in the temperature range from room temperature to 1000 °C. The results show that the krypton bubbles appeared at ~700 °C, and their size increased with increasing temperatures. The grain size and shape of the irradiated Zr-4 substrate changed with increasing temperature, and finally, columnar crystals appeared, which was related to the compressive stress induced via irradiation. The Cr₂Zr C14 phases formed at both the interface and the substrate at 700 °C and 1000 °C. Moreover, the accelerated failure process of irradiated Cr coating at high temperatures was observed via in situ TEM analysis.